Even if said descendants are male line descendants and have helped lead Greece independence war?
Time and distance. Thomas' descendants weren't living in Greece AFAIK (and that was back then, what incentive would they have to move back there now?). That said, Thomas apparently did still have legitimate issue as of the 19th century, however, the descent (Princes Isaac (b.1806) and Abraham (b.1812) living in England) had been excluded from the Byzantine succession due to the fact that they had at some point (Prince Manuel (b.1455) married a Turkish princess and whose sons, Ioannes and Andreas, (from whom their descent derived) converted to Islam. So I'm pretty sure the Greeks are gonna be going 'este mi kakos?' in why they should accept
that claimant (Isaac or Abraham) over some other European royal who actually means something.