Because 1. The amount of time and effort you would have to dedicate as an individual to get a complete Anima weapon I feel is appropriately comparable to the amount of time a static will have to put into A4S alone in order to even come close to a clear.
A Raider has to find 7 other like-minded players around their same skill level, work out a proper schedule with those players to take time out of their lives every week to play said content, spend time thinking about their itemization, party composition, working out a fight by fight strategies to make up for their group's strengths and weaknesses and then put in the blood, sweet, and tears and overall improve as a player or die trying.
After they accomplish all that maybe they'll actually clear A4S and then their group will eventually be awarded with an overabundance of 210 weapons. Every active player at level 60 also had this option available to them for 5 months prior to the release of this questline.
Someone gunning for an Anima weapon has to
Fate grind an alt class for maybe a day, run some unsynced dungeons, properly do their dailies every day, and put some time back into Alexander normal and eventually they can see themselves with a shiny new 210 weapon in like maybe 2 weeks to a month depending on how much time they feel like playing video games.
And 2. It is 100% true that this grind is very mild in comparison to other games on the market.
Let me compare that grind to the other current relevant weapon grind in my life, Phantasy Star Online 2's Austere weapons.
To obtain an Austere weapon, debatably the best weapons depending on the weapon type you're gunning for you have to:
collect 100 chunky chungas stones from the boss "Profound Darkness". This boss will only show up at pre-scheduled times and you get to fight him once per sever every time he shows up. You will on average get maybe 5 stones per kill. Next up collect 100 "Excubes", that part's easy done worry about that. So after about 15 Profound Darkness kills (You get some bonus chungas stones through title rewards) you are finally free to get an "Invade" weapon of your choice!
That's not an Austere.
Now after obtaining an Invade weapon, you have to collect 100 more stones from Profound Darkness, but on top of that you need to collect 100 Nero stones as well. Nero stones from from PD and any other "Dark Falz" variant in the game, it's not a 100% drop and you can at most maybe get 3 Nero stones per Falz kill if you are super lucky. You also need to collect 50 stones from clearing Ultimate difficulty in three different zones, getting maybe 3 stones per clear. You also need to get 5 stones from clearing the three different sets of Extreme quests, so 15 stones from XQs total. Finally after all that, you hand over 300 more Excubes and destroy your Invade weapon and you are given a half upgraded Austere weapon.
Now repeat that entire process again, and you have a fully upgraded Austere weapon for one of 17 different weapons.