Question

Why do the passengers in high-altitude jet planes feel the

sensation of weight while passengers in the International Space Station do not?

Answer 1

High-altitude airplanes aren't going nearly fast enough. You have to have a little bit of understanding of how orbits work:

When something is in orbit, it's essentially always falling towards the Earth. It's being pulled by gravity with almost the same force as anything on the ground... however, it's going at such a high speed parallel to the surface that gravity just slightly bends its path downward instead of pulling it straight down. If it's going fast enough, this bent path will be a circle with a radius greater than the Earth (or an ellipse, but that gets a little more complicated). So you're still being affected by gravity, it's just that you and the spaceship you're in are falling at the same speed. Like if you were put in an elevator-sized room and dropped out of an airplane, you'd float in the room because you're falling at the same rate.

To reach low earth orbit (LEO), you need to be traveling about 17,000mph, and even faster for higher orbits. Even the fastest manned planes in the world can only go about 2,500 mph, and standard passenger jets only go about 650mph. Not nearly fast enough to reach orbit.