Why is the MAX8 still flying?

The FAA grounding allows each airframe to be flown three times on ferry flights. Perhaps airlines are moving them to bases where maintenance can be carried out while they're not flying.

The FA database could be wrong. If you do a B78M search on FR24 you won't find a single plane in the air

there are at least 9 SWA to 7 different locations, so ferry flights seem dubious. Maybe, but doubtful. It is a mystery.

Yes, the -600, -700, -800, and -900 are all Next Generation aircraft. The MAX-7, MAX-8, and MAX-9 are the updated variants of the respective NG variants, from my understanding. Many of the -700 and -800 have a split-style winglet similar, but not identical to the MAX, which uses an all-new split winglet. Biggest difference between the NG and MAX at a glance is the APU come at the tail. On the NG, the tail of the fuselage blends into fhe profile of the rudder as it always has on the 737. On the MAX, it’s an actual tailcone that extends aft of the rudder. L

MAX is the machine that uses the new MCAS system, developed due to the increased thrust of the LEAP1b engines. NG is the previous generation aircraft, no MCAS, equipped with the CFM-56 engines.

See my comment below ...