1) it's a poor investment of your time - the number of hours required to get big quads is massive compared to ~15minutes of squatting 3x per week.
2) some cyclists just never get big quads even though they're spectacularly powerful - a lot of the juniors at the track i race at who are faster than me (generally speaking, they have a higher power to weight AND have better efficiency) are relatively tiny. It's hard to build muscle when you're training 10-15hours a week so i guess a lot of the strength they have comes from neuromuscular (CNS) rather than just sheer, inefficient cross sectional area (like me).
3) the track sprinters are all squatting anyway - it's pretty standard for an world level track sprinter to be able to squat out a few reps of 2 to 2.5x their body weight.
but, if you have time to kill, by all means give it a go. it will probably bear fruit, but i doubt it's the most efficient way to do it. i guess you've got to ask yourself if you have the time and energy to commit to riding a bike that you can't possibly use for squatting...