It's pretty common. If the site isn't about to be turned into the foundations of a new supermarket (This is a common fate for archaeological sites), you can't just leave an open pit behind. People might fall in! Plus everything deteriorates faster when exposed to the elements. Erecting a building to protect the site might be a nice idea... If you had a lot of money and nothing else to do with it. Some ruins will attract tourists if you build a nice museum around them, but most are too uninteresting or remote to attract enough people to make this worthwhile.
Reburying sites is standard practice. They survived hundreds or thousands of years buried under dirt, so putting the dirt back may help preserve them for hundreds or thousands of years more.
Another practice that may surprise you is that archaeologists often dig up only parts of a site, deliberately. i.e. They'll leave some parts where they think there's something interesting untouched. They do this because digging is a destructive process. Any information that can be gleaned from digging up a site has to be done with the technology and methods of the day. Archaeologists of the future might be able to learn substantially more than archaeologists of today from the same column of earth. So, you dig up only part of the site and leave other parts completely untouched so that future archaeologists can return and learn things you couldn't.
One very common justification archaeologists give for their field existing beyond heritage preservation is that it can help inform our own responses to future events. Archaeology/history is our only long-term view of societies and how they've adapted to changing conditions historically.
The actual application of that research remains a bit limited though.
It doesn't necessarily have to have a direct future-looking application; just comprehending why things are the way they are today, has value in itself - particularly in the political sphere.
Reburying sites is standard practice. They survived hundreds or thousands of years buried under dirt, so putting the dirt back may help preserve them for hundreds or thousands of years more.
Another practice that may surprise you is that archaeologists often dig up only parts of a site, deliberately. i.e. They'll leave some parts where they think there's something interesting untouched. They do this because digging is a destructive process. Any information that can be gleaned from digging up a site has to be done with the technology and methods of the day. Archaeologists of the future might be able to learn substantially more than archaeologists of today from the same column of earth. So, you dig up only part of the site and leave other parts completely untouched so that future archaeologists can return and learn things you couldn't.