Fees can be a big reason for smaller amounts.

Simplicity, e.g. when you need to load up sats for a day trip without understanding the intricacies of each self custody wallet.

Usually access to a wider range of feautures, e.g. when some services only send payments to an lnaddress, I can quickly fire up a custodial wallet to receive it.

Also ease of onboarding in general. Lightning has a very steep learning curve, so I find good to have something I can start using right away and expand my skillset over time.