1) Small engines can be temperamental (I hate when dandelion fluff can cause a dead stick)
4) Smaller/lighter flight packs are too expensive
5) I'm doubtful about a good performing "full house" 1/2a aircraft
6) wing loading too high for 3d
7) Severely limited by weather (what I consider light breezes for my other planes (<20 knots) is rather extreme for these little things)
8) Bigger simply flys better
9) I keep losing them under stuff in my workshop/car/fingernail

Seriously, I had a 1/2A heli (LMH), went to a 30 size, incredible difference. Now I have a 60 size, another order of increased pleasure. When I can afford it, I'll get a big gasser.

I've owned and flown many 1/2As fixed wing aircraft. There is a certain kind of fun and convenience but, I'm afraid they'll never be much more than an occasional distraction for me. A 'small plane' by my definition is anything under a .46