Replies to your questions are good. I'd say the yield downside is the most glaring. Farmers really can't afford a have a self-imposed 'bad' year while they try to adopt new practices. Bankers and lenders (which farmers rely on for operating loans might not even approve--IDK). It absolutely takes some trial and error as no 2 farms are the same. This also hurts testing things out in a smaller scale on your farm. You need to borrow/rent equipment or buy the equipment. But when you buy equipment without the scale, it basically adds overhead (with additional risk to the downside for yields).
People don't like to admit it, but yields under current intense monoculture, fertilizer happy are best-case scenario. This is obvious and intended, we're squeezing as much yield as possible without care for long-term consequences. Those yields might not be achievable under regenerative practices (but they might be in certain farms). For some reason, we have this mindset where we can't give up any yield, but in reality, if the economic models and government subsidies were redesigned, we absolutely could.