If you shoot cast lead bullets, the 30-30 has all the case capacity you can use. If you shoot cast lead in a 308, then you're having to work on the problem of how to get a consistent load with less than a full case of powder.
I'm one who shoots 100 rounds at the range for fun for every 1 round I shoot at game. Heck, make that 250.
So one good reason for the 30-30 is I can rip through 100 rounds, spend only $15, and have a great time at the range on the cheap. Did you know that if you get your bullet in just the right place under a grapefruit size rock, you can pop it several feet in the air? Now that's a useful skill, right there.
As a bonus, it makes a great round for my early teenage grandsons to hunt deer with. If they can get within 150 yards, they can slay Bambi and not end up with a flinch from too much recoil and muzzle blast.
