This, basically.

Also, as others have mentioned, the ludicrously inflated budget of making blockbuster movies/games are partly to blame for this.

The hideously bloated budgets require these games/movies to be huge hits. And, to quote the Simpsons: "The easiest way to be popular is to leech off the popularity of others." This is where the little word "brand recognition" comes in.

Ever wondered why they made a movie out of "Battleship"? Brand recognition. The same goes for remakes/reboots of popular games or movies. When you watch remakes of yore, like Cronenberg's "The Fly", "Invasion of the Body Snatchers", "Assault on Precinct 13" (which is a remake of "Rio Bravo"), "Scarface", you'll notice that they will be immensely different, often only taking the basic idea of the original film and taking it in a radically new direction. Today's remakes, on the other hand, feel more like "same shit, but streamlined to conform to the audiovisual conventions of today's cinema). In the minds of the moneymen, brand recognition garantuees a financial success (or at least minimizes the threat of financial failure).

Because AAA games are expensive as hell and the publishers want all the points be in its favor. A famous or recognized brand/franchise/intellectual property is one of them...

All of the above.

Well Kermit, because it's an easy and almost assured way of making money.

Didn't both of those bomb at the box office? The sad thing is that a lot of the ticket sales are coming from fans of the original films, who buy a ticket fully aware that it will suck, but they want to see it anyway, so no one on the internet can accuse them of not having seen it first, only to have their negative preconceptions about the remake fulfilled.

I've heard that there will be a remake of Starship Troopers too. Foolishness! Nothing could improve a Paul Verhoeven film!

because it's cheap

Also : there is no reason.

I do realise it has happened in the past but it sure feels like it happens a lot more often now (to new levels) and repeatedly for certain franchises...:/

As long as everybody's favourite dirty dutchman is at the helm, I'd pay to see that in the cinema! Twice!

Because they sell. That's really all there is to it.

I can think of a lot of ways to make Starship Troopers better. The main one being a director that has actually read the book. For another give me damn jumpsuits with mini-nukes. A real cast and not some 90210 B-list actors. No love interest needed, this is supposed to be an Action flick - Marine/Army recruiting at it's finest.

There is another reason that is not that "bad".

I guess writers, directors, hell even members of the cast were fans of some franchises as kids/young adults and maybe still are. It is totally understandable for those people to want to have a go at telling their own version of the story. To take a bow in front of the original and let loose their own fantasies. It's the big budget version of fan fiction.

Take Pirates of the Caribbean: It's basically a reboot of all the pirate movies of old. And it's awesome, since you really can feel that they had a lot of fun making it.

Better yet: it's a "reboot" of a friggin' Disneyland ride! :o
(again, the wonders of brand recognition are at play here)

The problem that I see is they are remaking the wrong movies, have the wrong cast/directors, dumb-down the original, add elements to make it a family friendly movie.
The only remake so far that I have seen that was decent was the Judge Dredd. I still wish it had a better actor...no one can be better for that role than Sly Stallone though he is beyond the age of the part.