Honestly there is no reason to be this old expansion expensive. Kingdom Come Deliverance, Witcher 3, Wolfenstein and Doom (bundle edition) are games that cost slightly less then 10€ and released around 6-7 years ago.
Jagged Alliance 2 expansion back released 20 years ago costs almost 10€ which makes no sense, especially since I got both original Jagged Alliance 2 and Wildfire for around 3 €. Why is Jagged Alliance 2: Business illogically and outrageously expensive?

Ask Interplay, they've even reduced the number and extent of discounts for all their titles recently.

It’s possible that they just don’t think of putting it on sale, because it’s doesn’t have the same success as JA2.

It's actually on sale right now, but it's still very expensive compared to the other Jagged Alliance 2 games.

That must come from the publisher, Interplay, because they didn’t publish the much more successful JA2 and still want their share, but still a stupid move imho. Having the same price tag as JA2 would probably give them much more sales, and much more income than their current policy.

Honestly, calling a difference of 6 euro "outrageous" when kids these days regularily pay
FIFTY bucks for bad, boring, bland games is just plain silly.
That's ONE starbucks coffee difference or even less!

The thing is, games from the same era are priced lower. Even the base JA2 game and Wildfire *combined* cost the same than Unfinished Business without discounts, and unlike UB, they actually get discounted frequently and with higher percentage. UB is not even played as often by the fans.

I'm actually more surprised that GOG still doesn't sell JA2 Gold (JA2 + UB)

Heck, a Starbucks coffee is that expensive ? I don’t think you chose the right example here ! The games are from different publishers, which probably explains no grouped offer can be made.

It used to be cheaper. In 2016 when I bought it, it had a regular price of 5.49 EUR, and I got it on sale for 0.59.