Why are 3.1 modems so expensive?

Why are 3.1 modems so expensive? My contract expires April 17th. I have 200 channels + 200 mbps internet. I have a TP-Link TC-7620 modem. I also got Linksys Velop AX 4200 3 pack on sale at bestbuy few days ago.

After my contract expires I will renegotiate. If I stay with 200mb I am fine but if I want 1gb internet I will need a 3.1 modem. Its only 20 bucks more a month so I might. However 3.1 modems are still 150+ dollars. But 3.1 came out in 2013. So why is it still so expensive?

And also my tplink modem says 680mb on the box. But according to comcast my device info it says only 370mb. Not 680. I called and they said hardwired only 370 not 680. Why half almost?

And if I jump from 200mb to 400mb then will my tplink modem will not work. Or it will just 370 so only 30 loss. I even spotted a new arris sb6190 modem 3.0 at target. It says 1.4gbps on the box but comcast says only 859mb. Why are they saying so low.

The lady on thr phone said my 370mb is hardwired and not wireless. But wired is faster than wireless is it not? So why are they saying a 1.4gb modem is only 859mb.

If my modem was really 680 and not 370 I could do the 600mb internet package and that is good enough. And then save 150 on a new modem. But if it really is only 370 I am that is not good. Is the fox wrong or are they just trying make me buy a new modem and spend more $$$.