But they wont. Huge sections of the Ultramarines Chapter (previous to Guilliman walking) felt that to disobey the Codex was to commit Heresy.
Then Wraith brought up supplies. In a Codex-compliant Chapter, I agree that it would be extremely unlikely that they'd have over 100 Heavy Bolters in their Armoury. They just don't need that many. So why would they have that many?