People usually choose custodial wallets for convenience and ease-of-use. It makes onboarding a new user a very simple process to show them that all they need to do is download/install an app on their phone and hit a "Receive" button to get bitcoin. There are plenty non-technical users that if they encountered anything more than that, would simply be unable to take Bitcoin seriously.

Unfortunately users who solely rely on custodial wallets are still facing severe risk in the form of incompetence on the wallet's part by leaking their data, or voluntarily sharing data with governments, or in the form of confiscation either by those government or through hacks. Centralized entities are easy targets for both governments and hackers, so custodial wallet users are placing a high degree of trust in that wallet and the organization behind it.

I think a better way to onboard new users would be to use wallets which allow the safe use of another person's Bitcoin node, but ideally your own. Samourai Wallet is the best-in-class for on-chain transactions since it gives you privacy options when spending. New users won't understand enough to think about that right away, but it's better for them overall if they're first familiar with it as a wallet. For Lightning, Phoenix or Muun (which isn't actually Lightning) would be a "good enough" first stop for a new user without the ability to run their own node, especially since you can use Phoenix over Tor (you can use Muun over tor via Orbot, but that would be far outside the ability of any new user).