Because you’re not buying any ‘local alarm’ and it’s not advertised as such. The real advantage is that you can control it and receive signals being anywhere, it has cellular and battery backup, it has billion of smart functions and options, it integrates with digital assistants, locks, cameras, it is expected to be a premium product by design, £8 pm or £80 pa is nothing for someone who buys the house and then equips it with premium price alarm and accessories and paying hundreds of pounds. You can always have a choice and still use your good, old Honeywell which works well and costs nothing.
And of course Ring Team Support member will not tell you this, so I hope I helped you understand what you are buying and why. Have a lovely day.