Why can’t they? New players don’t usually spend money on a dying game, old players don’t even need to. It’s not like SD would be losing much by eliminating a lot of the grind at this point. They’re losing players now, and at least this way they might bring in a few more to extend the life of the game by a little bit (and the change of someone buying an obsidian or whatever).
At a certain point you’re just pulling a Lawbreakers. That game was on a fast track to the gutter but it took them until it was all but dead to make it free, at which point it was too late. Might as well do something now, since DB is going that way too
Giving players a free item is a valid marketing strategy. It gives people some investment into a game, even if they’ve never played it. It doesn’t matter if you think crates should be in the game at all, because they are, and there are people who care about them.
Simply, free items pull in players. Players who might learn to like the game for more than just items.