About the buses.
Its true that if you choose between two gaps you are more likely to choose the larger one, however even in your illustration, most points in the time frame occupy one of the shorter gaps (the total length of short gaps is larger than the large gap), so you are more likely to arrive at one of the smaller gaps.
It still needs explaining, why the result of non uniform distribution of between-bus times always leads to worse average waiting time.

About the buses.

Its true that if you choose between two gaps you are more likely to choose the larger one, however even in your illustration, most points in the time frame occupy one of the shorter gaps (the total length of short gaps is larger than the large gap), so you are more likely to arrive at one of the smaller gaps.

It still needs explaining, why the result of non uniform distribution of between-bus times always leads to worse average waiting time.