Nah submarine cables have tons and tons of capacity. Fibre is super efficient and you can even use multiple colors to add capacity (DWDM). Radio spectrum is much more limited. Also they don't just lay one fibre at a time. Each fibre has its own clean broad spectrum where radio is always shared.

Sats will not replace them for backhaul. The capacity isn't there. For limited emergencies sure but not for all our Netflix.

This is all great for users in poorly connected areas and that's what it's really for.

Ps: also the sat link is more for remote areas, the network is much more efficient when an uplink is available in the same area and this is also how it provides near cable-like latency. Basically a bent-pipe system. If you'd use this capability for long-distance back haul you'd need to tie up a lot of sats' capacity increasing latency and decreasing capacity overall.