There are many motives that drive humans in being creative. Only one of them is a desire to make money. When this desire is portrayed (or even enforced) as the only legitimate motive for being creative, things tend to degrade to "least effort (and consequent low quality) for most profit". Read about the demise of PFI in Britain, as well as similar scenarios eslewhere, for an illustration of this. The international Art market is another variety of degradation-through-profit-addiction.
But those creators who create for the love of creating (and several other non-pecuniary motives) still have cost overheads. It would be no bad thing if we users of their creations could contribute to these overheads - the cost of software, computing resources and so forth. Creators could continue to create to their high standards, out of the joy of doing so, with no worries about it emptying their wallets if they don' sell sell sell.
Trainzkuidindex is a small realisation of such a scheme, perhaps.
Incidentally, I don't claim that any enterprise that makes a profit is automatically bad. Many enterprises have a multiplicity of motives additional to their profit motive - the desire for quality, utility of product, improvement of life and so forth. Sadly, such enterprises are becoming fewer, as the accountants sneer at anything not increasing the bottom line to max-black.
But I digress.
In addition to the cost overheads, the ever-accelerating changes to the software base of Trainz requires a steeper and steeper learning curve. Would profit-making stimulate creators to learn faster? Perhaps in some cases; but learning is also a form of creation and many like to learn new things for the sake of learning them, with all the associated pleasures and skills acquired, not least the ability to be persistent.
NV3 seem intent on "upgrading" (that dreaded word in modern life) at an ever accelerating pace. This pace seems to create more bugs and glitches for all, including creators. Still ... that's modernity for you, especially in the domain of technology.
Lataxe, happy to contribute to a Creators' Fund, as well as coughing up for the odd bit of payware.