I think the main difference is that you're probably focusing on a longer term than I am.

I do think we [humankind] need to get rid of our reliance on petrochemicals, but that process might take centuries; in the meantime, if the tech in the OP gets well developed, we might see the benefits already in our lifetimes. One thing doesn't exclude the other, so I think we should be chasing both.

With that in mind:

All of the alternatives are not being used today because it’s more expensive. And they’re more expensive because they don’t have a century of research dedicated to make them cheaper like oil has.

Kind of.

Hydrogen from electrolysis is expensive because it relies on huge amounts of electricity; and unless the electricity itself is "clean", we're simply shifting the problem elsewhere (e.g. burning natural gas for electricity for hydrogen, instead of simply reacting that natural gas with water). So we actually need to wait until clean electricity becomes even cheaper to solve this.

IMO we should rely more on legumes for nitrogen fixation, but I don't think it'll fix (eh) the issue completely. Also note that ammonia isn't just fertilisers, it's also everywhere in the industry, from cleaning agents to cooling systems. (It sucks in comparison with CFC, but at least it doesn't leave a hole in the ozone layer.)

People used to mine sulphur. It costs more, it's hell for the workers, and deposits aren't that common.

Ethylene is used almost everywhere in the industry. Not just for fruit ripening and polymers; pharmaceuticals, solvents, even detergent uses it. It's one of those building blocks in organic chemistry, alongside benzene and inorg junk. Industrially it's also used to produce ethanol; and while you can produce ethanol from biomass instead, you'll either need to

1. Rely even more on big sugarcane farms, like the ones responsible for the initial desertification of the Brazilian Northeast. (Sugarcane fucks the environment.)
2. Produce it from maize and other grains. Supply and demand, again - it makes them even more expensive.

Also note how this interacts with the ammonia issue. Like any other plant-based solution; they're still encouraging monoculture.

We don’t NEED oil. It’s just more convenient, it allows us not to change the status quo, to not think about different ways we should live. With oil, we can put our head in the sand and pretend we’re not careening to our own demise.

Currently we need it to keep our current life standards, and I don't think most people are willing to give up. And while I do think we [humans] should stop pretending we're digging our own collective grave, some things are only practical in the long run, but we still need to do things to help out in the short run.

(And by "we" I don't even mean those parasites wasting resources so they can say "I'm an astronaut now!" or wasting resources to build huge memecoin "mining" rigs. We'd solve a lot of the issue if we got rid of them first.)