Yes let's put a pin in all the thumb-sucking numbers of yours for now...
The revaluation is irrelevant to the argument. Before the deal went through, many here pointed out that the company is overvalued. Funnily enough you had articles, and some posters here, saying he should be paying more

The release about twitter fudging the numbers, which forms the basis of the reevaluation, came out long before that though. In other words those advertising on twitter did not care about this fact. Neither did they care right up until the deal became more finalised.
If you do ad buys and you see an return on investment on such you continue doing so. The actual revaluation, which did not occur until some time after the purchase, could not factor into their decision making. Regardless, the reevaluation did not occur due to Musks purchase, but rather what was exposed later on. Now bear in mind that these things were already at play when the advertisers were apparently "happy" with the returns on their ad buys.
Considering all this and the rhetoric leading up to the purchase, it's safe to say that these decisions were ideological in nature coupled with the fact that the economy was on a downward spiral.
The only other legitimate reason for pulling ads is when the systems to do so becomes unavailable. This wasn't applicable at that point even if it may be true later on.