I've given up trying to understand what's going on in Eccleston's head. On the one hand my understanding is that Big Finish simply can't pay big money, even to get an actual modern Doctor on board. When I met with one of their producers he basically implied that Tennant had to keep overriding his agent to ensure he was still being offered BF work, and that Matt's agent was very against him doing BF. So I doubt he's doing BF for the money. At least not directly.
Obviously where he is likely raking it in is at the conventions. That's relatively easy money and a whole lot of it.
The question is, has Eccleston softened on Who because he realises how much money he can make off it, or has his experiences with BF and fans at conventions softened him on Who and the money's just coincidental?
To stress I have no problem with actors making money from conventions, but CE's attitude tends to rub me up the wrong way. The notion that he won't come back to be part of an ensemble but expects his own episode/series plays into that.
It is possible to believe that he was poorly treated by RTD etc back in the day, but also accept that maybe he doesn't play well with others. Wasn't there some Dr Who related thang in the early days of the pandemic and everyone was involved in promoting some concert or other, except Eccleston who insisted on doing his own thing? Edit to add, just checked it was the Big Night celebrating NHS workers, a short film featuring every living Doctor...except one! Eccleston instead read a poem on the One Show.
