From a gameplay standpoint, Pokemon designed for the early game tend not to have super powerful moves or abilities for the sake of encouraging diverse team rosters and experimenting with new Pokemon and other options. Not many people would wait most of the game to replace their flying type if their current flying type was already excellent. Restrictive movepools helps to encourage trying out new team members. The Starly evolution live is another example. They have good attack and speed, a fairly good ability and two strong endgame moves in Brave Bird and Close Combat. Good, but nothing special. They're perfectly usable and even strong, but there are still options that with proper investment could outclass it.
From a design standpoint, it's possible that it's just to do with Talonflame's nature. Talonflame is built around speed. Attacks like Flare Blitz and Brave Bird can easily be imagined as Talonflame cloaking itself in it's power before crashing at great velocity to deal maximum damage, but sustaining injury in the process. Even it's ability, Gale Wings, supports this, providing speedy priority to it's flying type attacks. Slower, less dramatic attacks don't really fit into this MO. Sky Attack is too slow and needs charging, which doesn't suit an ultra fast bird. And hurricane doesn't suit the image of an ultra fast crash landing jet monster either. Just speculation though I'm afraid.
Tl;Dr Speculation about not making early mons too good so people will try out more options, and Talonflame being built for speed suiting it's current movepool.
