agreed, never understood the point of transit visas; It’s either you are allowed landside or you are not. Needing a visa to stay at the airport to only to go landisde for several hours is a bit pointless.
A number of countries require these in the case of pax from the usual list of countries. Mainly (at last in Europe) has to do with trying to stop people from staying in the transit country as an asylum seeker/refugee, etc.