Yes – if you want to use a mobile network, just just a 4G router and use that, or a satilite connection but they’re very expensive and unreliable compared to using the telephone network or cable TV network.
Ultimately, someone, somewhere is going to have to run a cable from a exchange to your house and they’ll have to maintain that network and everyone has to pay their little bit to maintain it.
They do themselves no favours by selling the virtue of the landline because no one under 40 use them anymore, but the OpenReach network is a telephone network and every line has a number – so they throw in the landline as it’s there anyway to try to ‘add value’.
You can have your own line installed if you want, you have to lease it – typically you’re looking at £3k-£5k instalation and about £500 a month lease costs – but you get very fast speeds.