That's an answer which hasn't had much thought applied to it. In the groups I've worked in, the problems with culture conditions were long appreciated. The factors entrenching the existing practices are largely down to: standardisation between laboratories, being able to publish (non-standard practices can be a large negative for reviewers), and cost (DMEM is cheap in liquid or powder form).

I've used specialist media for endothelial cells, and stem cells of various types (human and mouse, embryonic and mesenchymal). It could be up to £200 for 500ml of culture media, with a shelf life of just a week once you'd added all the frozen supplements. This makes things very costly once you scale things up.

But culture media are only the beginning of the problem. Another source of big problems are the culture conditions. Standard incubator conditions used everywhere are 37.5°C, 5% CO₂, 100% humidity. However, this is not remotely realistic, and is actively damaging to most cell types. The 5% CO₂ keeps the pH in balance (the media contains buffers). But the other 95% is regular atmosphere containing ~20.9% O₂, so the effective concentration is ~19.9% O₂. But the physiological oxygen concentration in the body's tissues is much less, a fraction of a percent.

One culture phenomenon is that "primary" cultures of isolated cells don't proliferate much, but after several "passages" they eventually become "established" and more proliferative (essentially, somewhat cancerous, and losing some of the characteristics of the original cell type). There is also a limit on the total number of passages the cells can withstand (all except the most aggressive cancer lines). This is largely down to cumulative DNA damage from oxygen. If you culture the same cells under low oxygen conditions, the cells don't become established, retain their characteristics, and can be cultured nearly indefinitely. Much more realistic. This can be done with an incubator with additional gas feeds and an oxygen sensor, which can purge the excess oxygen with N₂ then add CO₂ to 5%.

Another problem is that the culture medium is static. The cells use up its nutrients and then sit in their own waste. It needs regular replacement. But this cycle of nutrient excess and deficit and waste accumulation isn't realistic either, and may also have profound effects upon cellular physiology. Tissues in the body are continually perfused by blood plasma, maintaining nutrient levels and removing waste. This is something else which researchers should be developing; in fact, developing such systems was a part of my PhD (an unsuccessful part, I should add; it's actually quite technically difficult to perfuse patterned 3D scaffolds). But doing this for flasks and plates is a much simpler problem.

So these three major areas (media, conditions, perfusion) all contain major deviations from physiological conditions which all have the potential to grossly affect research outcomes. The fact that we have all collectively stuck with what worked for over 50 years is somewhat outrageous, particularly when for the first two there are commercial solutions which could be used today, but most people ignore. That's lazy. None of it is a "money-making scheme", though there would certainly be opportunities for media and equipment vendors.