Many reasons. 1st of all who told you they are using them at “home anyways”? Maybe they use them while commuting, in the office, while traveling, cycling, gym, whatever.
Also even at home, I cannot imagine not laying down in bed with earphones immersed in the music. Absolutely atrocious to wear a huge open back headphones making me very uncomfortable on the pillow. IEMS OBLITERATE full size headphones with that alone, no competition whatsoever. Also they are much lighter and can be worn for longer periods ergonomy wise, and I actually even enjoy the additional isolation even while at home vs open back headphones, it gives me even more “intimate” and that private feeling while listening to music. Not exactly living in a countryside, so there is always some sort of noise even with windows closed.
Anyways, those are just a few reasons why there is not even competition, IEMS b very far superior for me
Ppl go crazy with any type of hobby, it consumes them and they get into a “problem” of collecting, and develop obsession with any topic they get into.
However, more than a single pair is normal. For example I have one full size open back headphones for enjoying music at home, one high end iems for listening on the go and in bed, and one semi-wireless for gym and cycling cos of convenience that I use with smartphone. Over 3 pairs for different purposes and I can genuinely see no point, but as I said, ppl get consumed by the hobby and that is true for any hobby pretty much.