If you're part of a software factory and only turn a psd into a html/css website then yes, knowing a programming language and doing backend doesn't help. If you

If you're part of a software factory and only turn a psd into a html/css website then yes, knowing a programming language and doing backend doesn't help. If you work at a company which sells expertise to others, then they will want you to be an expert at something. If you work on a product team then it really helps to know a bit of everything, architecture, writing frontends, writing apis, databases, designing scalable services, managing hundreds of servers and other infra through automation, ci/cd, data engineering, ux, testing, talking to users, talking to stakeholders, gathering requirements, managing a project, managing yourself. From time to time you may ask the help of an expert.