Letscher portrayed Reverse-Flash for a hot minute on The Flash and for a stint on DC’s Legends of Tomorrow, but eventually Tom Cavanagh reprised his role as the villain.
The reason, as heard in the crossover “Crisis on Earth-X” was simply because Thawne liked that face better.
Plus, as I mentioned earlier, Reverse-Flash has never actually been a Wells.
Eobard Thawne changed his own face to look like Earth 1’s Harrison Wells, and later reverted back to his original face played by Matt Letscher.