A repeated failure in teams I see is not setting aside time for improving performance. They are running a 100%+ on feature delivery and not picking up the items that make delivery faster and less risky.

The main culprit I've seen for causing this is the "agile" ways of working.

Back in Waterfall days there was a huge lull when things "went to test" where you could mentally relax and pick up improvement efforts while Suaron's eye wasn't fixed on your team.

Agile, and Kanban, messed this up by making teams fully under Sauron's eye and feeling the pressure to be constantly delivering.

How does technical debt build-up? One day at a time

This way of working has led to building up of technical debt in teams that can't be fixed in a pay as you go style. I recommend that you should allocate percentages of your time to delivering feature improvements and dealing with ad-hoc demand.

Keep a regular backlog of items that improve your ability to release, or avoid technical risks that will impact your customers.

Only in times of extreme pressure would I expect the allocation to be 100% on feature delivery.

Aim for 20% on your 'delivery performance' budget so when you need to do the extra work you have slack built into your system to handle it.