Ok let me give you an example.
Let’s say I get 500€ for an interior visualization. I get a steady stream of work, so as soon as I finished one project I can start on the next one. I can model all the chairs, sofas, beds, everything, for every single scene, time and time again. unwrap, do cloth sim, PBR textures, everything. I can do that. Or I can buy a couple of archviz assets for 700€-1000€, the costs of which I will have recouped in 2 projects and which is tax deductible anyway, and just assemble the scenes, speeding up my workflow, allowing me to be more productive, earning more.
This is just archviz as an example but it applies for everything you get paid for. Not even in 3D but in every line of work. Why spend money on a new computer to render 2 minutes faster? You could just have a coffee instead.
The answer is that (human) time is the costliest factor of all and even tough I have the skills to model everything myself I won’t do it until it is absolutely necessary and then I will make sure to get paid the time it takes.
Do you think a paying client cares if you modeled everything yourself? And if he does, he’s better paying for it or you are putting yourself out of business.
I’d like to make models and sell them, I just can’t understand why would professionals (since average joe’s don’t use cgtrader and such) even buy them, if they are perfectly capable of creating the same models for free.
Let’s say you build an asset, it takes you 5 hours. You’d like to earn 50€ per hour of your work, so you have to earn at least 250€ for selling this asset. You put it on gumroad for 10€ and hope to sell it at least 25 times to break even, everything after that is profit. If you are living somewhere where 10€ per hours is much, or even less, then all the better for you.
Let’s assume I can model the same asset faster than you, because I am so damn professional It takes me 2 hours. I value my time the same as you do, 50€ per hour. So I can spend 100€ of my time to do it myself or buy yours for 10€. Easy choice, isn’t it?
Now you also see why it is important to always be busy and to have the next thing to work on (and get paid for). Turnover is key.
But not all assets are created the same, I’ll gladly spend money on them but they have to be premium quality. For example a chair is often not simpy a chair but a specific producer, modeled to measurements. Add quality unwrapping and texturing to that and it takes quite some time.