Yeah, but if the they did not intervene in the markets then interest rates would probably be below zero.
I don't think there's any PPT active in the market, but I do think that central banks like the BoJ buying ETFs and the Swiss National Bank buying equities with printed francs (in their quest to keep the CHF tied to EUR) has a good deal to do with the market's resiliency. I'm sure other central banks are active participants as well.
The PTT is not active every day in the market - there purpose is not to make a perma bull market. The PTT is at the disposal of the president for urgent times. If you had bought the market the moment presidents have advised the public that it is a good time to buy the market like in the Bush post 911 and Obama post subprime crash you would be well rewarded. Bear markets reversed to the minute of the announcements making huge parabolic moves. A crashed market + the president utilizing the PTT = announcement public should get in = all reward/no risk. There is no stronger buy signal.