>The Mueller investigation still resulted in 34 individuals being charged.
So: the Obama administration had almost 8 months (from the time Trump locked down the primary in early June, to the inauguration the following January) to dig into Trump, and the Mueller investigation was 18 (?) months long. The United States, and the United states government, has plenty of people who want to take Trump down; we can assume from what some of them have said on the record about Trump that a subset of those people is strongly motivated. It is clear that people within government have been comfortable leaking information unfavourable to Trump, and it was clear during the previous administration that agencies (notably: the IRS) are staffed with some people generally hostile to Republicans and Republican causes and willing to act on a partisan basis.
With the full powers of the US government during the Obama administration's kick at the can, and all the power brought to bear by the not-Trump-sympathetic investigators on Mueller's team, and all the other people in the US government who might be able to get their hands on information (eg. transcripts of meetings, tax returns), and Trump's notoriously loose-lipped personality, and the threat of prison hanging over a handful of his close associates, etc, etc, all that squeezed out was a handful of process and other unrelated (eg. fraud) crimes. And the election interference crimes occurred during the Obama administration's watch, and they admitted they knew about at least some of the attempts and elected to go soft. But Trump is the one giving the Russians an easy pass, not Mr The-'80s-wants-its-foreign-policy-back, I'll-have-more-flexibility-after-my-re-election. Some perspective is in order.
Some people may wish there's still a stone there to be turned over.