The market is now thinking the deal wouldn't go through especially after all the negativity, push back from investors, and analyst downgrades. That explains the price action today.
What they and many on the forums don't know yet is that it has already been decided. The decision was made, even before they went public with it. SolarCity is deader than the turkey you had for last years thanksgiving. It can't be allowed to go bust and this is the only way out for them. I personally don't mind it since many have their entire net worth tied to SCTY stock.
Elon really wants this done and its already been decided. If he knew there was even a 1% chance of not passing he wouldn't have recused himself of the voting, because there isn't any other option. Either a buyout or SCTY insolvency (Lost reputation, lost net worth, margin call, SpaceX bonds, harder for TSLA to raise money in the future, 20% or more drop in TSLA stock price, SCTY shares used as collateral would have to be made whole with TSLA shares taking Elon's ownership in TSLA lower and that causes more selling). I can go all day on how this affects TSLA shareholders. All the voting, due diligence etc is for show. I would think that major holders have already been informed weeks ago and they have agreed to voting "Yes"
The sooner everyone realizes this and moves on, the better. The deal is going to happen, because it has already happened even before the first time you heard of it.
Regarding why they they couldn't wait until the share price is much lower? Well, if they waited till the share price was in the single digits then it would be clearly obvious it was a bailout (can't claim BS synergies anymore) plus TSLA investors would not be OK with buying a near death company.