People are doing t7s because of the interaction with Abyss Spires and the league mechanic. If you aren’t interested in farming this specific strat, it is probably better to farm the highest-tier maps you can reliably clear.
Is it better to farm T/7 or T/16 maps in POE 3.23 Affliction?
The T7 strat revolves around the fact that fighting lots of rares is the best way to “cash out” on juiced maps due to the possibility of the hidden conversion mods they might have (resulting in the currency, scarab, and 6-link explosions).
So the way you get a huge amount of rares in your map is through the abyss. If you follow an abyss all the way through you get one of three results: a chest, abyssal depths, and a spire. The only one that matters is the spire, as the drops from the chest are mostly irrelevant and the abyssal depths are another zone, so it doesn’t use the juice you put in. The reason the spires are so good is because they throw out a projectile that spawns a rare, and the spire can be affected by projectile modifiers. So the strategy is to get as many extra projectiles on enemies as possible, by rolling additional projectiles on the map and using wandering to increase the effect of the map mods to get even more projectiles. Then there are also the purple wisps that also make mobs empowered by it to shoot additional projectiles.
In the end, you have a spire that will be shooting out 6-7 rare monsters every so often. And then you use magic find to get your rewards.
Now the big reason why this Strat is done on T7 is because there you can guarantee that every single abyss will end up in a spire. You start by using gilded abyss scarabs, as they not only guarantee an abyss spawning, but it makes so that it will end in a spire or abyssal depths. But you see, the abyssal depths require a certain level of the zone to spawn, so by running lower-level content, you guarantee that every abyss you find ends up in a spire.
Also, T11s may give you a 10% chance for an abyssal depth instead of a spire, but it'll also give you a chance to drop Valdos puzzle boxes. So we'd say it's kinda still worth it as a strategy if you do it higher.
All in all, the strategy is also kinda exhausting and fills the screen with super tanky monsters. And requires fairly pricey scarabs and compasses. So consider whether you wanna deal with that when there are plenty of simpler farming strategies out there.