Ekans, Arbok, Mankey, Poliwhirl, Slowpoke, Chansey, Pineco, Dunsparce, Snubbull, Shuckle, Teddiursa, Corsola, Tyrogue, Vigoroth, Loudred, Makuhita, Aron, Spheal, Bronzor, Riolu, Croagunk, Mantyke, Dwebble, Tirtouga, Archen.
A list of all the pokemon who are considerably weaker, and in most cases weigh much less than Beartic, that learn Earthquake.
There's a whole boatload that can learn it, but I didn't list some of the other, more, "questionable" pokemon that can learn it, since everyone's opinion on the others could differ, whereas the above list, I hope we can agree, that there is no justification in those learning Earthquake while Beartic cannot. The "mass =/= strength" point holds no weight (lol) here, as all are weaker and have less mass.
So what exactly allows them to learn Earthquake while Beartic cannot? O_o Maybe GF didn't want Beartic to have a similar movepool as Ursaring, idk.