The router is more of a server. Pihole is just an example (and yes a $35 pi would be plenty for it) but I have many old servers running all kinds of other things so I decided to update and consolidate some of this.
More importantly, I and many geeks I know but/bought several when a new model first comes out because they are (were) cheap but electronics wholesalers don’t offer free shipping so it makes sense to buy as many as you think you’ll use (until the next one comes out) in one go to minimize the amortized cost.
I miscalculated and ended up using all of mine, but I have friends that still have some of their stock.