Well I think that even in the magical world of Star Wars there are some real-world concerns that these guys have to worry about.
All of these massive spaceships no doubt cost tons of money to produce and acquire--there's even a line in this film about the Rebellion buying weapons from the same people the First Order gets theirs from--so they don't exactly grow on trees. To lose one is to lose a huge investment, especially for a small, cash-strapped group that's on the brink of extinction, and if they just go ramming their ships into the First Order's ships on a consistent basis, it won't be long before they have no ships left. Then what?
Maybe it would make some sense if the Rebellion was the larger, dominant organization but that's clearly not the case. They're a ragtag group of rabble-rousers and by this point there's not much left of them.
I think what's important to understand about the moment in the movie is that they were about to lose that ship anyway. That ship was fucked, there was no saving it, hence the evacuation. In that moment the decision to sacrifice it made sense only because it was about to either be destroyed or captured by the enemy.
