I suspect the sudden drop in availability and prices for cargo missions may have been unintentional, and revealed a fundamental problem with the BGS. Otherwise they could have it fixed in a day.
All economies, even socialist, depend on the movement of capital. When a large number of players decide to start taking passenger missions, the flow of cargo drops. But the demand is still there so either the local economies tank, or they have to raise prices for the cargo missions to compensate. Instead, prices dropped. If Fdev fixes this, then they have to worry about over-inflation. Then they'd have to raise the prices on ships and modules. Fixing the BGS to avoid wild swings in prices, and still have some realistic effects on local economies, might not be that easy.
Yes, this would explain a lot. Because they added a vast number of passenger missions promissing millions, they potentially (although these missions won't be popular, taking several hours at least) over-inflated the market... Although if this is the case, they should have seen that coming...