[Ajedi32]

Yes, in most cases coercion isn't as obvious as someone literally pointing a gun to your head (though in some cases it could be, there's nothing to prevent it). Typically it'll be something more subtle, like the "vote bribing" scenarios you outlined, but with the added pressure of the person providing the incentive literally being able to stand over your shoulder and watch you fill out the ballot, then take the envelope from you and deposit it themselves into a drop box.

As I've said before, coercion doesn't need to be overt to be effective. Just a small amount of social pressure applied over a large number of people is enough to make a significant difference. That's why typically there are laws banning campaigning right outside polling places. Now what if the "polling place" is the entire country, over a period of multiple weeks? How are you going to enforce that?

Consider also that the electorate being able to trust that elections are free and fair is nearly as important as them actually being so. Its not enough to just say "that's probably not happening at sufficient scale to make a difference"; you need to be able to convincingly demonstrate to voters it actually isn't. Having a system that's robust to these types of cheating schemes (as in-person, secret paper ballot elections have been for centuries past) is the best way I know to do that.