adding a subplot to a story can add to the complexity and interest, and give the readers more to latch onto, whatever that subplot is. however it has to be done right.
i dont think stories without love interests are lacking in any way - look at moana, look at brave, look at, idk, ghostbusters? they can in fact be a refreshing change from the status quo of shoehorning a (typically heterosexual) romantic subplot into a story where it has insufficient development and often involves sexist tropes.
on the other hand, if you do it right, and you do it because you want to, and think its right for the characters it can add to the personal connection with the characters, raise the stakes, provide relief from intense mainplot, and be a lot of fun to write.
typically, i find, gay people prefer same sex relationships and straight people prefer opposite. which... makes sense. theres also like 'fujoshis' and that but being straight and obsessing over gay relationships is a liiiiil weird so lets ignore them
as a lesbian, i know that i roll my eyes and lose interest oftentimes with heterosexual relationships in media, and id get very excited if a story had a gay or lesbian couple. however, theres lots of m/f romances in media i really like, because theyre charming characters and the romance has been well executed.
i also know a lot of feminist women - regardless of sexuality - can be suspicious of the introduction of a heterosexual love interest because of aforementioned sexist tropes. but thats just a case of doing your romantic subplot properly, and being original.