I read both third and first person all the time! I do think it's a little harder for an author to get first person to attract my attention, but I'll click out of a fic for all sorts of reasons (failure to punctuate dialogue, anyone calling Hermione 'Mione, etc) so it's not a slam on the tense or POV itself, in general.

I think that when the canon is first person, like Rivers of London, it's a lot more accepted and often expected.