Nope you are not alone.
Work can be tough at whatever level you operate although wherever you sit in the corporate hierarchy you think everyone else's position is easier - well, at least I did until I got a bit older and wiser.
I've never had a traditional 9-5 standard hours job and tbh I think that must be tough - the sheer repetition must be hard to handle. I've never had a poorly paid job and the thought of going to work just to struggle to make ends meet (or even worse - not) must be gruelling. And I've never had a job that demands high levels of physical effort - that must take it's toll over the years too. Nor have I had a job eg a neurosurgeon who daily deals with 'life my hands situations' - the sheer stress of that must be tremendous. So, irrespective of what you do, I guess it all grinds you down.
Coupled to this is the inevitability of the loss of ambition, the diminishing need to win and an ever growing feeling of ke sera sera that seems to be a common denominator of those of us who are entering the later stages of life.
So yes, I guess most people have less to give to work as their career chugs on - they've been used, abused, chewed up and in some cases spit out of the workplace.
For me the novelties of corporate life wore thin, I remember my first company car being a big moment, the first time I stayed in a hotel on expenses, my first expense account, my first big job, travelling first class on planes & trains, getting my own office, my own PA, being responsible for a whole business not just a part, getting stock options etc - of course it was much more than that over the years but these were the retrospectively shallow things that fired me up along the way and helped keep the grinding down at bay.
And then, one day, you look around and think **** (insert expletive of choice) and wonder where your life went. For me the last few years of my career was an incessant round of Board / Planning / Budgeting / Review / Governance yada yada yada meetings, 60000 miles a year at the helm of a car, umpteen train & plane trips and virtually seven days a week working. This is the stark reality of running a business despite the rewards that go with it.
Notwithstanding the above once I 'got away' I realised that some components of my working life were vital for my well-being - I quite like the challenge of running an enterprise and I really love meeting/talking to people. So, whilst I understand why some people don't understand why it is possible to not want to be completely retired, for me, and many others, there is something satisfying about being able to fulfil certain needs and potter along doing something on your own terms and at your own pace.
Last year I worked a whopping 800 hours.
Got fairly well paid for it too but, more importantly, it fills a couple of otherwise blank pages in this chapter of my life.