I think back to when I graduated from college. I finished before laptops were required. Email was still a fairly new thing, in fact I had one of the first email addresses from my university.
I started a job where I was given a pager to wear on my hip. This pager could receive text messages only from people with the same type of pager device. These were furnished by RIM (later renamed Blackberry after its most iconic product). That's right, I had the predecessor to the Blackberry. In technology years it's almost like I told you I knew your great grandfather's grandfather.
I had a cell phone that's only function was making phone calls. I didn't text, send email or even take pictures with this thing. It was a flip phone.
I barely knew the Microsoft suite of products except for Word when I wrote papers in the university computer lab.
There was no YouTube and people were still using Yahoo as a search engine.
I had never managed a single person, not even myself very well up to this point.
Over the next 15 years I became a superuser of all things technology. I grew and managed a department of people. I received an MBA. I started my own business.
None of those things would have been possible without continuous growth in hard and soft skills outside of my company offerings.
If you're still questioning why professional development matters I'm going to assume you fell asleep somewhere around the blackberry part of the story. Scroll back up on your Android or Iphone and reread this. ;-)