The downside is that it is not real grass.
It doesn’t absorb heat and sound.
It reflects sunlight.
It does not absorb carbon dioxide and pump out fresh oxygen like a normal lawn.
It cannot be repaired with a handful of soil seed and small bad of soil. When it’s done, it’s done.
It is not nearly as nice to walk on. It’s not a cool soft bed on a sunny day.
You can’t throw waste water on it.
The good stuff is VERY expensive!!!
Those are just off the top of my head.
Basically, it all boils down to the simple fact that it’s not real.
Also keep in mind the many benefits of good artificial grass
Many other problems come from getting cheap turf or turf that’s poorly installed, but for the good stuff there are many benefits that in some cases outway the costs.