There's really no such thing as "passive income." There's legitimate income and then there's income from scams, like MLMs and Ponzis. With investing and lending you still need to exercise extreme diligence in order to make a profit, so I wouldn't call those "passive" either.

The whole point of using Lightning is that its faster and cheaper than on-chain transactions. If you set your channel fee too high people will bypass it and you will make less income than you did by setting a low fee. If the cost of doing a lightning transaction supersedes that of an on-chain transaction, people will simply revert to transacting on-chain.

Also, its not overly simple to set up and maintain your own lightning node (though it is a lot easier today than it used to be). Maintaining a consistent internet connection, having to pay for that and the electricity of running your computer also need to be factored into the overall cost.