Default [Q] How do the gsm/umts/lte/cdma technologies work with frequencies?

Why do certain phones support just specific bands for each technology, gms/lte/umts and the like? I don't see why the phone cannot just recieve signals from a range of frequencies then usuing different technologies to read the frequencies at each level. Like some phones support the 1700/2100 lte band but don't support the 1700/2100 on umts/gsm? Are the phones just locked for the different frequencies on those technology due to corporations?