I have a standard answer I give when people ask why I don't pursue being a professional critic. It's basically my lack of desire to review movies that I don't have a strong opinion on. I occasionally try it and you can find some examples around.
It's more complicated than that, however. There are also movies that I don't think I can add anything to the general discourse on. I mean, what can I say about Notes on a Scandal? Judi Dench is terrific? Cate Blanchett having sex with a 15 year old is hot... I mean, uh... creepy. But anyway, who consults me on this? If you were, then, yes, go ahead a check it out.
The only time I struggle past not having anything I either really want to say or some perspective I have that's unique is with movies I'd like to make more people aware of... great obscure movies, interesting failures or what-have-you. I assume this is what's largely expected of me. It's certainly what I have the time and patience for.