But a senior has more experience with the "why" behind the coding. What are the requirements in terms of schedule, user experience, stability, maintainability, performance, development process, QA, etc. A junior can be great at one of these, but a senior has to take responsibility for all of them. So you need to understand the needs of all the stakeholders outside the dev team. (At least the basics; functional details deserve an expert of their own.)
(Yet all the interviews I turn up to these days want an hour and a half timed coding challenge to be completed).
I think an interview that focuses on coding challenges isn't really looking for a senior. Point them to a junior that's more appropriate to their needs.
In most interviews I do, we do talk about abstractions and maintainability and stuff like that. Although I have recently done one that involved a coding kata, which was kind of interesting because during the kata we also moved through a couple of (small scale) levels of abstraction while discussing them, and particularly the appropriate time to abstract some stuff.