Mages have always been a popular archetype in League of Legends. Already because their historical position is on the midlane, the most popular role in the game despite the fact that it is not necessarily the most powerful in soloQ and among the pros. It is true that it has always been difficult to see many different mages at the same time on the midlane in a meta. Generally there are a few who dominate, and it is much rarer to come across the others. Yet even taking this into account, their popularity has declined greatly.
Whether on the professional scene or in soloQ, mid bruisers and assassins have gradually pushed mages out of their lane of choice. So much so that today, if we except the mage or even the two mages who are doing well on certain patches, it is much more common to see them succeed on the botlane as a support than on the midlane. The archetype was still popular during Worlds with the Azir/Sylas/Viktor trio, but this was also largely due to the domination of very aggressive botlanes (Lucian/Nami in the lead), the mage therefore becoming a little l team's late game insurance .
Where does the problem come from ?
Several avenues can be explored. The first is that mages like the midlane have undergone little change in their approach to the game in recent seasons (minion xp nerfs certainly have a big impact, but it doesn't change the general gameplay much). Then, they ended up having very few new items despite the appearance of mythicals, where the other archetypes were better served. Finally, it is now generally faster to buy AD than AP, and in addition 1 AD costs less than 1 AP. The more time passes, the fewer arguments the mages have to dominate the game.
Statements from Riot Games
Riot Axes has given some clarification on this subject. "That AP is more expensive than AD is weird, but it's not necessarily a problem. If players were given the option to buy AP faster or in larger quantities, it most of the spell ratios would then have to be nerfed. Although personally, I am rather in favor of making it easier to buy AP, it is not an easy decision to put in place". It is true that this track could solve part of the problem , by allowing mages to snowball more effectively, since the gold gains would have more impact. However, it could also make mage players feel useless if their lane phase goes wrong.
"More than doing a total overhaul for the archetype, we would have to take care of the mages on a case-by-case basis. Of course we see that there are modifications to be made about them, but we don't have nothing special planned for the moment. Nevertheless we are aware that there is a problem with this archetype, but until we really have a solution that seems relevant to us, we are not promising anything.