EF couldn't keep all of their best riders because pandemics hit the main sponsor really hard for obvious reasons.I was a little surprised that EF didn't try to make him their marquee GT rider to replace Uran but I think (again, maybe wrong) that his move to Ineos came at a time when EF had very little money.
Still, I think someone wrote on the forum that Vaughters had a choice to keep either Carthy or Martinez and with hindsight, I think Martinez was probably a better choice, But that was in 2020, when Carthy was on the Vuelta podium, so I guess it wasn't that obvious back then.