I'm pretty sure 4G/LTE antennas add quite a bit of cost to manufacture the SOC that powers the phone.Yeah budget Lumia phones have weird restrictions. There's a newer Lumia 530 or 535 coming out and it has everything and I believe it's the same price or cheaper than mine, except that it's 3g only. Why? I have no idea.
Most sub 200 dollar phones, the low end Lumias and the Moto E and G are actually made for large emerging markets like Brazil and India where they have no 4G/LTE networks, so putting those antennas on the SOC is a pointless waste.