The plan can only be deliberate, egregious price discrimination. I found out about it because T-Mobile was heavily advertising it on their website. So I tried to sign up. You can't do that; you have to either order a SIM card from them (which is free), or get one from Walmart. I tried to get a SIM card from the local T-Mobile store. They don't sell those. I ordered a SIM card online and had to wait a week. When it arrived, I activated it on (surprise!) the T-Mobile website. I guess you can do that after all.

Note that in ordering the SIM card I did not indicate that I wanted any particular plan. The $30 plan just "happened" to be available for that card.

Was I willing to wait for one week in order to lower the bill for a large recurring cost by 40%? Yes. But T-Mobile seems to be gambling that most people aren't.