1. I read that FEMA sent about 6 truck mounted generators to TX. I have no idea how accurate this info was but it doesn't really matter. If every portable generator in the the US was sent it wouldn't have been enough.
2. TX is area wise too large to rapidly insert generators into every corner and the capacity is too large. The area of TX is about the same size as Germany. About 3/4 of the state was affected by the snow and ice. The whole state plus northern Mexico was affected by the cold and blackouts. Note that the TX grid also includes a large slice of eastern OK. OK was colder and snowier than TX. Most of TX had 1 storm. Most OK had 2 storms. Give Okies some love - They coped.
3. FEMA can respond after the disaster is over with, not while it is ongoing. The first days of a disaster, people and local governments are on their own.
My opinions...
If Trump was still President all media would be blaming him for the cold weather in Texas.