you're right! There are 4tb and 5tb drives out there but they have to double the platters to get that kind of capacity .... 500mb-2tb 7mm & 4tb-5tb 15mm
WD offers 1tb in 9,5mm as a WD BLACK @ 7.200rpm
Seagate offers 2tb in 7mm as a Seagate Firecuder @ 5.400rpm + 8GB intelligent Cache (SSHD)