Until relatively recently - 2017, to be specific - someone on H1B who lost their job had no grace period to find other employment under the law. Enforcement was another matter, so many people chanced it regardless - but the concern is that overstaying one's visa can have significant consequences for your ability to get new ones long into the future if found out.

In 2017, USCIS unilaterally enacted a 60-day grace period as an administrative rule, which is still in effect today. But, given the current US job market in tech, 60 days may not be sufficient.

Twitter aside, it should also be noted that, being an administrative rule, it can be changed fairly easily for political reasons, since it doesn't have to go through Congress, and courts generally err on the side of executive agencies' judgment on such matters.