It’s the approach more than anything - similar to Monzo in the fact you can open and run the account exclusively from your phone, except it’s aimed at limited companies.
Took me about 2 weeks to sign up for a business current account from a “traditional” bank (a further month until my account was eligible for a debit card…). Tide was set up on the same day, card received very quickly after that.
Traditional banks can also tend to charge per-transfer fees in addition to a set monthly fee; Tide has pretty reasonable transfer fees but with no recurring banking fee, which can be nicer for a small startup.