Meller found TONS of evidence of collusion between Trump and the Russians . . .
Actually, the Mueller report was not able to determine "that members of the Trump campaign conspired or coordinated with the Russian government in its [2016] election interference activities."
The Mueller lawyers did develop evidence, sufficient to meet a
prima facie burden in any court in the United States, that Trump and his associates engaged in a criminal attempt to obstruct the
investigation into Russian interference in that election. However, in accordance with U.S. Department of Justice policy, the Mueller report deferred to the congressional impeachment authority for the initial disposition of the evidence rather than recommending prosecution of an incumbent president. Trump could be criminally prosecuted now for the alleged obstruction of justice since he no longer is in office.
Interesting similarity to Richard Nixon. There was never sufficient evidence to demonstrate that Nixon was involved in the planning of the Watergate burglary. The charges that led to his impeachment and resignation were based on his involvement in the subsequent obstruction of justice (as well as other, earlier, arguably criminal behavior).