Simplifying for time and because I'm retarded: no-bid ties into basics of supply/demand. The more people want something, the more they're willing to pay. On the other hand, if people don't want what you're selling, you either have to hold the bag or lower the price until someone wants it. Literally no one wants MBS right now at their current price because they're recognized as being a toxic time bomb about to go off. So you either get a race to the bottom in terms of price or the seller holding onto some nasty bags.
The real problem is that one of the main MBS sellers is the fed as part of their proposed QT. They need to sell this stuff and no one wants it. That'll lead to a lot of market problems, but as for us, if this goes down like it did in 2008, what you can expect is a lot of people whose mortgages now cost more than their house. The housing bubble will pop.