Railway tracks aren't privitised and haven't been for 20 years. The trains running on them were - at least until covid broke everything
The problem is that the government let companies like Virgin off when they broke their contract, allowing them to bid high, take the profits, then walk away rather than fulfilling their contracted duties. Privatise the profits, socialise the losses.
Nethertheless there is tons of competition on transport in the UK
1) To get from Birmingham to London you can choose 3 different rail providers giving 3 different cost/value returns. Faster more frequent ones cost more.
2) On top of that you can also take a coach, hire a car, drive your own car, or of course not travel at all
3) Manchester to London you can fly, take the coach, drive (car hire or your own car), take three different trains ranging from £50 return and 3 hours to £180 return and 2 hours.
"Railway tracks" isn't where the competition is, transport is, and there's tons of competition. I remember I used to commute from a commuter town into Manchester. I could take the train during the peak, or I could take it off peak, or I could take the slower train from a different company, or I could drive, or I could take a commuter bus.
When it comes to the last mile of say BT, you used to have a monopoly, it would take months to get a replacement handset connected. Today though "a phone line" isn't what you want, internet is, and there are options
1) BT/Opeanreach connection (fibre or copper)
2) Non-BT fibre (in many cities)
3) Wireless ISPs
4) Satelite ISPs (Starlink/Oneweb or Geostationary)
Each has benefits and drawbacks
I would agree that the last mile of water and possibly electric provision shouldn't have been privitised. Treatment works though -- why not? There's no real limit on the number you can have.
When it comes to long distance electric again why not. There is a lot of money to be made transporting Electricity in Scotland and selling it to the south east. Let multiple companies do that.
The problem is planning permission and nimbyism means it's impossible to actually build new lines.