Almost every manager I know does tasks that they should have others do.
The same people are time poor and try to do too much. Without exception, when they learn to delegate effectively, they create time to become better leaders.
There are lots of reasons people give why they don't delegate, but in reality, they are excuses. "By the time I show someone how to do something, I could have done it myself" is a common one.
Delegating means getting things off your plate so you can make your highest value contribution to your organisation. It also means that you are giving others a chance to develop.
Saying to someone "I used to do this task, but I think you are ready for more responsibility", then showing support and trust, means it is likely they will step up and free you up. It's win-win.
I am giving away my CREST Effective Delegation guide. Email me for a copy.