I keep running into Astro running Shields in Farm PTs as a SCH. (Why?)

[Deceptus]

I had an AST in my FC back at the end of Heavensward who wouldn't switch to Diurnal when paired with a SCH. When I asked why she said "AST shields are better." While I don't think that that's the truth now or was even back then

There was a time when the base AST shield was better than the base Adlo and was instant cast.