Having just gotten out of a role like this: It's not.
It punishes doing backend / infra, tech debt, planning, or any work that isn't customer-facing (ie: stuff your senior+ engineers typically are expected to do). The demo day audience is largely non-technical people rather than it being a technical demo.
If you spent the sprint, or a large part of it, helping others or laying the groundwork for future projects with a company that treats demos like you've stated, you'll quickly push out anyone who is doing anything but blindly working on product.
I didn't leave / get pushed out because of the above, the cycle and meeting-heavy schedule drove me up the wall frankly.