Why are most stars we see in the sky main-sequence stars?

Answer 1

In a word: statistics. Just as most people you meet are of average height, and if you took a poll you'd find they are of "average" intelligence, the main-sequence stars represent the average star out there.

They are large to fuse light elements to produce enough light to reach our planet; while remaining small to have a life-span that will enable the light to reach our planet. This in turn effects their brightness. Too bright, they're burning too hot and will supernova soon. Too dim, we won't see them as they're not undergoing enough fusion to produce the energy and light to reach this far into space.

Answer 2

We live in an epoch when the majority of stars are middle-aged, which means most of them are main sequence. Take another look in about 5-billion years and the ratio will start leaning towards fewer main sequence stars. Ultimately, if the universe is infinite--as it appears to be--the time will come when virtually all stars will be unstable red giants nearing the end of their lives.

Answer 3

Is that true? Stars spend three-fourths or more of their lives on the main sequence, so you would expect main sequence stars to be more numerous, but giants are much brighter and therefore a much larger proportion of them are visible.

Looking over a list of the 50 brightest stars, I count only 14 main sequence stars (Roman numeral V after spectral type), and several of those are secondaries of giants.