1. I think he gets a decent amount of credit,
2. The Stock Market DID crash right after him, and then we had the Depression and WWII after that, so his presidency is overshadowed by not one but TWO of our more famous presidents--
The famously "bad" (or at least commonly seen as bad) Herbert Hoover...
...and the longest-serving President in our history (thanks to an Amendment, he'll hold that record for the foreseeable future) who is often ranked in the Top 5, FDR.
(And I know some here don't care for him...but I'm sorry...I like FDR, and you can't deny the man generally DOES rank in the Top 5 and generally is held to be one of our greats...the Republicans often tout Lincoln and Reagan--and with good reason, though I have to say that to rank the latter anywhere near the former, as some do, is absurd--and the Democrats often tout FDR and JFK...so Coolidge gets lost in the shuffle.)
What's more,
3. He was known as a very, very quiet man, still and stiff, and history loves characters (maybe the most famous quip about Coolidge comes from the great feminist author Dorothy Parker--when informed Coolidge had died, she famously remarked, "How could they tell?")
;)