How does T-mobile get away with charging $20 for a new SIM because I didn't buy a phone at their store when they overcharge $130 for a phone google sells unlocked for $300(nexus 4)

I'm upgrading from an old blackberry that uses a standard SIM, and because they changed to a pay as you go business model right before I was eligible for an upgrade I opted for a cheap Nexus 4. Tmobile is charging $430 for the same model that google sells direct for $300 unlocked with no bloatware which I'm assuming Tmobile loads it with and charges more. I opted to buy it for $300 and because I need a new SIM and didn't buy it overpriced I have to pay an additional $20 for a microsim.

I've been a t-mobile customer for almost a decade and getting real tired of their shenanigans. Am I the only one that has noticed this skeevy business model?