I'm not entirely sure why. I just try to keep games fun and interesting! If a game is not quite fun enough, a little rule modification or careful deal making is obviously in order. But some people call that creativity 'infuriating.'
I guess it's because I have a long history of 'adapting' games. When we were younger, my brother and I constantly modified game rules. Well, mostly I modified them. Sometimes we played games of monopoly where we both ended up with 15k and substantial hotel strips. We gave each other free rent all the time -- it was Philanthropist Monopoly, where you really just tried to accumulate as much money as possibly. We'd have to convert $1 bills to $1000 bills, or use 10k bills from other monopoly type games. Another childhood game we modified the rules to was "Hit each other with big sticks." If you're a guy, you've probably played some variation of this game. I have some friends who played "hit each other with 2x4s" which I suppose you'd call "eXtremE childhood games." I modified the game to include 6 foot pipe insulation so there was less chance of actual injury, and a greater chance of convincing my 4 year younger brother that he really did have a chance.
So while some people call my monopoly deals frustrating, they're really done out of good intentions. I think it's really just my creative part expressing itself, trying to make life more interesting. If you're not particularly good at creating your own house rules, it's ok -- you can learn. I found a guide to help you out. Try it!