Nope. Sierra was bought by Activision and while Activision and Blizzard have merged, they still act as separate companies. Hence why, despite Activision being ever-present on Steam, Blizzard is nowhere to be seen outside their store. Let's not forget that Activision is already here.
And while Mechwarrior 1+2 might have been published by Activision, Mechwarrior 3 was published by Microprose and 4 by Microsoft. Alas, at least for Mechwarrior 1+2, the biggest problem is the licensing which involves IPs that are not Battletech, thus making a rerelease even more difficult than your typical licensed game (which is already hard enough).

Ok, so where's the problem with Earthsiege 1+2 and Starsiege then? Not enough interest by GoG?

Who knows, really? Maybe it's a technical problem, maybe GOG's and Activision's lawyers are trying to work out a new deal to finally start releasing more games after 3 years, maybe GOG is delaying it to focus on other games, maybe I don't know shit. :P

At least on surface, there doesn't seem to be any particularly damning reason for their absence.

Burst through the door

Someone said Mechwarrior?!

Looks at link

YEAH!

I'd love a more tactical game than the shadowruns. I really like those, but they feel a bit too much streamlined.

Or maybe because FASA Interactive and all IP to BattleTech (incl. MechWarrior) belongs to Microsoft.

Earthsiege 2 aren't Battletech products.

Yeap somehow I know that. For some reason I thought we were discussing BattleTech here, my bad.

Well, as for Mechwarrior, I wouldn't consider 3 and 4 an impossibility, at least no more an impossibility than other licensed games and it helps that Mechwarrior 4 itself was published by Microsoft. No idea who owns Mechwarrior 3, maybe Atari, but I'm not 100% sure about that.

published [url=https://en.wikipedia.org/wiki/MechWarrior_3]MW 3 in 1999

What makes turn base mecha games unique?

Is there any different between a turn based mecha game from any other war games?

The mecha could be another tank with robot skin. You can just research, and upgrade your tanks all the same.

Or that foot solider that can upgrade it armor vest, guns, bio enhancement, exo-skeleton.just like a mecha upgrade guns, and armor and engine.

Is that the story, back ground, environment? But the gameplay will be alike?

Yup. In turn, Microprose was purchased by Hasbro Interactive and Hasbro Interactive was purchased by Infogrames, which renamed itself to the current Atari. In addition, the Gold Edition of Mechwarrior 3 was published by Infogrames.

hell lets ask for Mech Commander ;)

while tanks are the closest we have to an actual analogue to a battlemech there are some differences. HBS seems fairly certain that they will have melee combat (something from the boardgame that was hardly if ever replicated in any of the video games) like punching or "death from above" ie using jumpjets to get above an enemy and use your own mech as a bomb.

while the the year is 3025 the 200 years of near constant warfare has pretty much beaten the explored galaxy "the Inner Sphere" stupid so bio enhancements (don't think this tech is known) & exo-skeletons if they exist should be a great rarity.

From a ludological historical perspective the interesting element was the thematic incorporation of heat as an action limiting factor. Modern warfare is very instantaneous, compare air combat with missiles at range from WW1 and WW2 dogfights. Batlletech might have been the first wargame system (in the sense you used the term) where the action point limitations made sense. These constraints both simplified systems and broadened the strategic depth (by making each decision more meaningful in itself rather than having meaning emerge as average of many decisions). Everything you do costs heat, so there is no instantaneous "I win" button, it's a naturally compensating system - the bigger and more powerful you are, the more heat you generate. Usually the tradeoff is between firepower and mobility of course, but that's precisely what modern technology breaks.

I could make a case for leadership systems being functionally similar and originated earlier, yet those always fell in some uncanny valley I think. Likely because of their origin in the period when complexity for the sake of complexity (rather for hyper simulationist goals) was all the rage. And now I think of it they are opposed to each other, leadership systems are usually a positive feedback loop, rather than a negative one. Better leader = more power (less ludological constraint), whereas better mech = more heat (more constraint). Hmmm and better leader is similar to the more experience loop in RPG's as well... whatever, I could go on for hours I think.

Theme is key also in how the sci fi setting was merged with an almost feudal setting. I'm actually quite sure that was intentional design as the parallels with medieval armored knights are very very apparent. And it worked since it made the setting very familiar and easy to jump in. Anyway those aspects to me were the meat that lead to Battletech's cult like status, on top of the giant robot bones.