Logical for who though?
It seems like a pretty sound business decision if they can make a single skin that people will spend 350$ on, in contrast with 100+ skins that players can't even spend money to buy if they wanted to.
Just doing a handful of skins at a time in order of popularity seems impractical, and all of the hardcore mains of other champs would likely be salty for quite some time as they waited their turn. Getting the skins distributed properly for those who unlock the appropriate mastery level before the skin is released compared to those who unlock it after also seems like a technical headache. (And even if people were relatively patient, it's still a huge investment, even if they spread it out over time.)
Loyal to the game and loyal to a particular champ are also separate things. The former could be addressed in a variety of ways (accounts over a certain age could get some free stuff, or accounts with certain play time, or even just making some super expensive 100k IP things in store that only the super dedicated could ever unlock), and it'd be reasonably feasible since it's just a one time investment. The latter though is a workload multiplied by 100+ to make it unique for each champion, plus it adds on additional work for every new champion going forward (as it doesn't take long for people to promptly main a new champ and churn out max mastery in record time).
Riots a pretty cool company and is pretty gamer oriented versus money grabbing (...for now), so I can see them wanting to do something cool like free skin(s) or similar for mastery instead of just churning out hextech crafting skins with an evil grin on their face, but the practicality of it is a pretty massive hurdle for them to realistically overcome. It'll be interesting to see what they do ultimately come up with for the future.