Gardner was the prior NRSC chair when they gained seats. That's the ONLY reason.
And a lousy one at that (half-hearted/no involvement in MT/WV/OH where Republicans were badly outspent/defined early, prioritizing AZ and especially NV over more winnable races, not pushing for Jenkins in WV, etc.). The headline shouldn’t have said "Republicans score big wins in Senate", it should have been "Republicans fail to lock Democrats out of Senate majority until 2022."
Their only impressive win was FL, and that had nothing to do with Gardner and everything with Scott's $$$/strengths as a candidate.