In my mind, 'tinkering for fun and knowledge' was never meant to be profitable - if you're tinkering with the express aim of making a profit i'm not sure you're really 'tinkering' so much as you're trying to create a product/service/output for someone else to pay for?

There's absolutely nothing wrong with doing that - I'm just not sure the 'ethos' of tinkering has anything to do with trying to make money and is usually reserved for describing someone playing about with something for their own enjoyment/fun with no desire to make money.

Now, of course some people did find that their tinkerings were able to make them money, but I think at its base it's a term I'd tend to say implies doing something for fun/for themselves, rather than doing it for profit?

In my experience there's still plenty of people out there tinkering just for their own personal satisfaction, but of course there's almost certain a whole load more people out there 'tinkering' to try make a profit.