So, your evidence shows that almost no one released tax returns before elected, let alone 10 years prior of tax returns?
Obama was already a state senator before we see his first return, and would have been happy to show that his income is little above his [comfortable] publicly-known salary.
Bill Clinton, even though spent years as a state governor, his first return wasn't released until after he was elected president, going by the website you provided.
George W Bush didn't release one prior to winning the presidency.
George Bush 1 didn't release one one until a decade after started being vp and, two years after winning the presidency.
And, still, their tax returns shows almost nothing about their wealth.
You speak from ignorance as you would in know that your statement is not true if you had clicked on the link and gone through the entire list. I decided I did not want to post 5 or 6 postings to cover the entire list.