I know nowadays that doesn’t matter as much due to most DVD players or disc drives being region free, but I recall the time when I was younger in the late 90’s to early 2000’s most discs were region locked based on where you bought a copy (basically the same as buying a Japanese N64 cartridge versus an US one) meaning they won’t work when in another country.
For instance: I’ve purchased the first 2 home alone movies in Japan during my trip back then when they’re re-released on DVD (encoded as NTSC) while I come from a country where most discs by default are PAL so they didn’t work on my normal DVD player, having to purchase a multi region DVD player just to watch them. (This was before streaming sites).
DVDs were released at different times in different countries or regions. Movie studios wanted to make sure they control those releases and you can’t just easily import and sell a bunch of DVDs from a region with an earlier release date.
Of course there were DVD players that let you switch regions infinitely (and eventually just play all regions) or some people who had a second player for another region, but those were, at least initially, outliers. To make the general public wait to buy DVDs from their region it worked.
Although, one could argue, it gave another advantage to piracy. Not only would a downloaded movie not threaten you with the FBI or make you sit through unskippable ads, they would be available as soon as their release in any one region, so you would have to wait (sometimes a lot) less.