I heard that was a result of them designing for certain thermal envelopes ahead of time and Intel then delivering chips that didn't meet the specs they were promised. Not sure is this is what happened though so take with a grain of salt.

If this was the case, one the one hand they should be criticized for releasing such bad laptops on the market but if they had already decided on developing their own silicon then maybe it made sense to just accept that some generations of Macbook were going to have thermal issues and focus all efforts on the future.

That would be excusable for a generation of macbooks. Not over multiple generations.