I really do think we are giving multitasking way more credit than it really deserves
If it's any consolation I think it's a lot to do with how society has been going. Like for a while there seemed to be a trend where bemoaning how exhausted you were was a badge of honour as it was "proof" that you were "productive". And then because people are cramming way too much in (because YOLO and "need to be productive every waking second" "doing anything possible to prove not lazy" whatever) "multitasking" becomes the way to cram everything and more into what time you have.
If it's a thing that comes natural then it's an amazing way of actually getting more done. If it's not or is something that you're currently working on, you may just end up feeling constantly burnt out and resentful and not actually be getting more done at best or even less at worst XD
Amusingly your ability to concentrate on one thing at a time and absorb it in its fullest is probably the goal of a lot of the people practising mindfulness.
Good luck with the audiobook + workout :D