Maybe it's politically motivated, but IMO so is the FAA's certification and nonaction so far. Boeing promised a software fix by January, and the FAA's decision not to ground the fleet was probably informally based on that promise. Unfortunately the software fix is proving more difficult than anticipated. Regulated, safety-critical software, whose failure leads to a smoking crater full of bodies can be like that. Especially in this case where it's not going to be just a bugfix, but probably a major redesign of the concept of the MCAS.

Ultimately though there are over 5000 orders for the 737MAX. The list price is $121 million. That makes the total value of the order book $600 Billion at list prices. That's roughly the market cap of Google or Apple, and the 737MAX is extremely important to the U.S. balance of trade. There is obviously going to be a political component to any big regulatory action on it.

The FAA needs to make a major course correction here, because what's even more important long-term than a single, very popular airplane to the U.S. economy is FAA's credibility as a regulator. In most countries, FAA certification means rubber-stamp certification from the local authority. As long as it is, it's a huge advantage to the U.S. aviation industry, because the FAA can write regs that are favorable to U.S. interests. This is only true though as long as the FAA is seen to have integrity.

In this case, when it comes to that, by my reading (and I'm not a lawyer or an expert), the MCAS is in violation of FAR part 25.672, and the 737MAX is not airworthy.