It's hard to understand what criteria the selectors are looking at sometimes - isn't it? Both Pearson and Clark had 11 year careers. Clark's numbers are superior in nearly every regard. More receptions, more yards, more TDs... and they were both spectacular in the playoffs (although Pearson had more playoff years in which to put up numbers).
If you just look at the numbers, it's a no-brainer. I'm not saying Pearson shouldn't be a HOFer. That discusssion has nothing to do with Gary Clark. But if you put him in, you absolutely have to put in Gary Clark.
I think Clark probably gets less focus because he played alongside Art Monk. My opinion, of those two guys, Clark was the better WR. It boggles the mind that he doesn't get more love. One could argue that getting selected in a 'Supplemental Draft' in 1984 and coming from a nearly unknown football school in James Madison University set him back in terms of getting due recognition and he just never recovered from that? But then you look at Pearson, who was signed at Tulsa as a QB and was later converted to WR. His college career was pretty yawn-worthy, and Dallas picked him up as an UDFA.
I'm not sure why HOF-worthy Redskins seem to have such a monumentally difficulty getting recognized by the HOF committee? But it definitely seems to be 'a thing'.