There are actually several factors at play here. The service takes its commission - usually 15-30% of the order amount, plus delivery is separate. Cafes add a markup specifically because they need to compensate for that commission, otherwise they're operating at a loss. So basically you're paying for the service itself as a middleman, for its logistics, for the courier to actually get to your area. And then inflation on top of that - prices on everything have gone up over the past three years, and that affects it too.
Plus, honestly, services like Yandex.Eda have been raising commissions for restaurants in recent years, especially if they're popular and know customers will order anyway. Cafes just pass those costs onto the price in the app - because they're getting fewer dine-in customers now, people prefer delivery. It's the simplest way to not end up in the red.
Also, there's the specifics of your particular area or how popular the cafe is. If delivery there costs more or there are tons of orders, the service might take a bigger cut, and the restaurant puts a higher markup accordingly. Basically, it's a combo of commissions, logistics, inflation, and business logic. If you wanna save money, calling the cafe directly and doing pickup - that's usually real savings.