Think of what 'HT' implies... Handi-talkie.
To be 'handie' you want to carry it.... more watts needs more power. Sure,.. you could get 10 watts from a Yaesu VX-7, but likely for only 2-5 minutes of use, else you'd have have external power.
Also - more power means more - heat. HT's have little in the means of expelling the heat generated for transmit.