i get u. but ur touching upon a big pile of worms that is mostly better left untouched if ur not an exceptional writer...
writing a story is already tough enough. would u as a writer brave the challenge of writing something completely new and original or back out to stick with something ur more familiar with and keep it simple?
for example if u have ur human character turn into a beastman would u simply make it have a human mind that struggles with its surroundings or would u add emphasis on how it has to constantly struggle to get used to being a different species? like fighting its urges to act less civilized, adapt to using its new body, and finding out the pros and cons of new body.
at that point it becomes a whole different story for a different audience.
sure it may be more entertaining but
the more complex it is the easier it is to screw up somewhere and boy do we have enough of stories that are riddled with holes.
theres also other avenues to consider such as 'how much would we as readers even care?'
u can detail ur beastman character to have four ears instead of two which gives them sharper hearing and better vertical sound localization. it sounds great to add on paper but most readers would simply prefer seeing 'they have better hearing' then move on with the story. of course this is assuming ur not an exceptional writer.
there can also be 'random' forced developments to 'spice things up' which i personally do not like.
ur beastman character can have bouts of bloodlust that pops up at the worst of times. as a reader u just know that its gonna happen at least once and most likely its not gonna have any big consequences.
uh. im sure i missed something but just do ur best not to think about how much more a story could have been