It didn’t help that 45 GOP House incumbents decided not to seek re-election in 2018.
The power of the incumbency is strong....a great many of these 45 would have been re-elected.
The silver lining is this....most of these GOP incumbents were RINOS.
You are correct, most of those who retired were Bush League Republicans.
They threw the House to the Democrats intentionally to stop Trump from reversing the Bush Plan for North Mexico (aka USA).