Mostly it's the drivers that have been striking, they tend to be an integrally important part of the trains moving.
While most of the train strikes over the last year have been RMT primarily, ASLEF and TSSA did vote to strike in support of RMT during the winter. They're both part of the TUC after all.
https://www.cityam.com/newest-strike-wave-to-hit-uk-as-platf...