The gravitational pull of the moon lifts up the ocean to cause tides. Well the Earth's gravitational pull is so strong on the moon that the heavier side of the moon always faces the Earth. This is called tidal locking. So the only way to ever see the far side of the moon is to go there. Humans have gone there before, but almost always during an Earth "full moon", which means the far side is unlit. We do have full images of the far side of the moon from remote probes, but the 21% of the far side that was lit had human eyes on it for the first time ever.
Moons get tidally locked because they're very close to their planet, so the planet's gravity is by far the strongest influence.
The planets have much more complicated gravitational interactions because in addition to the Sun's gravity, they influence each other. So you end up with things like orbital resonances instead.
A planet that's close to its star and far from other strong gravitational influences will tidally lock to the star.
wikipedia's explanation works for uniform bodies, yours doesn't. And since tidal bulges seem to be symmetric, there's no away to explain away the deformation as making one side heavier
It's because Earth pulls on the bulge in the Moon created by Earth's gravity.
It has to do with the tides. Except in this case it isn't ocean tides - it's lunar tides. Just as the Moon's gravity creates a bulge in Earth's oceans, Earth's gravity creates a bulge in the material that makes up the moon.
If Earth and the Moon didn't rotate, the bulges would "point" directly at the other body. But with rotation, the tidal bulge is a little bit offset in the direction of rotation. And the Moon used to rotate.
That offset creates a torque. Earth's gravity tries to pull the bulge into perfect alignment. Over time this slows the rotation of the moon until it stopped rotating at all.
(Technically the Moon does rotate, but it does so at the same rate that it orbits Earth. So it doesn't rotate from our perspective.)
I believe it's caused by even the slightest imbalance in mass. Because the moon is so close to Earth, the imbalance causes gravity to be slightly stronger on one side than the other side. Eventually, that leads to no rotation at all.
I imagine most bodies rotating around a second object will eventually lose their angular velocity.
To add: this happens because the parts of the Moon that are closer to the Earth are pulled in more by Earth's gravity, compared to the ones further away.
Consider what it'd mean if there were parts of the Earth that could not be seen from the moon, it would also mean those locations could never themselves see the moon.
Ignoring the orbital period implications, I think it'd be bigger news if either US or Europe, or Asia couldn't ever actually see the moon.
It may one day be, far in the future, although that's predicted to be so far off that Sol might have become a red giant by then, making the issue moot.
But only Luna is tidally locked at the moment. Terra is not, and its rotation still has a long way to slow down before it becomes so.
If you are on the near side of the moon[1], you will always see Earth see around Earth as it rotates and as the moon orbits it. You will also see it in different phases, like how we see lunar phases from Earth. If you are on the far side of the moon, you will not see Earth at all as you will always be facing away from it.
[1] The Earth does move in the moon's sky a bit. If you are on the near side but getting close to the far side, the Earth will be below the horizon sometimes.
