I won't try to give all the answers. Each point you mention has been discussed many times before, at great length. You could try searching "Steam" for example.
I could make a few points though, before instantly unsubscribing from the thread as I don't want to start answering questions.
If financial growth was the aim, LFS would have been a completely different game. Eric and I founded Live for Speed with a deliberate aim to work on our own project, free from the pressures and issues of working in a larger company. Admittedly, we thought it would just be a project of a year or two, so that looks a bit different more than two decades later.
Live for Speed was on sale before Steam existed, so this is why we have our own payment system. Moving to Steam at this point would require restructuring our business and changing the code model. We would then be at the mercy of Steam ratings and in my opinion no longer "independent" (even if Steam is said to be for indie developers, such 'independent' developers are entirely dependent on Steam). This is too long a subject and I won't get involved. Many pages of forum text have been written about this already.
Regarding income, Eric and I believe that the ability to work on what we like, in our own time, is more important than a high income. If we wanted a high income, it would have been better to stay employed in larger companies. However, there was a period of relatively high income for some time starting with the release of S2. But over some years, sales dropped off gradually until income was eventually too low to live on. Some of this was caused by my change in life, moving house and bringing up two small children, which affected development. By the way, they are now 18 and 16 years old. Another cause for the eventual drop off was the well documented piracy, in which pirates were able to create a bigger active community than the legitimate one.
There were some boosts in that time, such as after important updates and the S3 license release. Although that only provided access to the laser scanned Rockingham track, people who upgraded to S3 did ensure continuing development. Eventually we were able to offer mods, which are not properly available in pirated systems.
How is all this relevant? Well, now we have enough income to pay our bills, so we can continue developing. We are still not interested in hiring more staff and moving into an office. I'm sure we are even less willing to do that now, after all these years working from home. There is no thought entering our minds to suddenly give up our entire work philosophy and try to get rich by running a company!