What Trump voters said when asked to compare his inauguration crowd with Obama’s

It's not that these people don't accept (that is, comprehend and agree with) basic facts. The photographic evidence is irrefutable.

The conclusion is necessarily that they're knowingly lying, which is something else entirely.

It'd be equivalent to showing someone a globe of the earth and asking them if the globe itself was flat or round, and their responding "flat" simply because that's the position of their team.