1. If you seek a job as a movie reviewer, seeing a lot of movies is A) something you presumably enjoy, and B) your job. I don't care how many movies they have to watch. It's their job.
2. To single out Ebert, specifically, his "critical analysis" is often a whim. It's like watching politicians. Pull a review/speech from 2 years ago and what they were praising then, they're bemoaning now, and vice versa.
3. If they seem like a pretentious snob, it's because (at least to me) they are pretentious snobs. I also know a duck when I see one, I know what food tastes good when I eat it, and I know when I've stepped in something squishy that smells bad. Sure, it's all subjective, but when 96% of the time their opinions are diametrically opposed to mine AND they have little or no consistency in the expression of their opinions, I can safely say that I find them to be useless.
The whole movie review "industry" is like that. Look at the Academy Awards. People win b/c it's "their turn", they win b/c of their gender, their race, or the political statements made as often as someone wins for a spectacular script or performance.