If it's still too vague, then I'll list the number one reason: a business standpoint. It can only stand to make them money. We know Capcom likes money.
That's only if it sells amazingly. Fans and even newcomers loved the RE1 remake on gamecube, but until it got remastered again just recently they made no hints at all about doing an RE2 remake. They didn't even START that remake until just a few short years ago. So no, it's not that simple for them at all. They could have done REmake 2 ages ago if it was such an easy answer, but they didn't.
It could very well be another 10+ years before RE3 remake might come around regardless of how well 2 sells.
I mean it'll still make them money regardless, so there's no reason why they wouldn't want to update the ending of the best three games in the series.
You mean 2,4 and 7 because 3 sure as hell isn't the best or top five even ---