Product Managers asked to perform Product Owner role

I have recently joined a start up where Product Managers are becoming frustrated as they are asked to perform also product owner's responsibilities and feel they have no time to work on more strategical and market focus role.

Context:

1.The team uses Kanban

2. PM are currently managing all ceremonies and some have two small product teams to manage.

3. The company has no budget for additional resources to perform scrum master or product owner responsibilities