[mthoms]

I suspect it’s because they want to verify they can withdraw from the account, not just deposit. Maybe they have deposit-only account links but IIRC the default is two-way. That’s because, for example, you can subscribe to various services using PayPal (if you have no funds in your PP account they will withdraw it from your bank account).

[Scoundreller]

This makes a lot of sense. Lots of advice in the early days of PayPal to have a separate account for them and keep nothing in it.