Every now and then they have a sale on Crowns. I've not heard of a similar sale for ESO+.
Also, until Crafting Bags came out the benefits for subbing were minimal--with the introduction of those, plus the release of more and more DLC, it's getting to be a better option. But for about a year prior to Imperial City coming out, there was nothing in the way of new DLC, so subbing perks consisted of...slightly more gold and XP. And Crowns you didn't have any DLC to spend on.
You don't need a credit card for eso+. You can also use paypal or simply buy game time cards.
The crown store is mostly for people who spend more than 1,5k crowns per month.
for people who don't have access to credit card perhaps?
Yes. I sub when new DLC comes out. I use my crowns for IC and mounts