Well, "why did so much coal form during the Carboniferous period" is an interesting question. One theory is that plants started to produce lignin (wood) and other novel compounds during that time, while fungi and bacteria had not yet evolved the ability to break them down. So lots of organic matter was piling up on the ground and not being released back into the atmosphere. (Fun related note, the oxygen level in the atmosphere rose to very high levels during this time, which enabled gigantism in insects and amphibians - organisms that depend on simple diffusion of oxygen for their respiratory system). Eventually all that organic matter could be buried and fossilized.
So anyway, since fungi and bacteria are more evolved today, it's unlikely that such massive buildup of organic matter would occur again. Any given burial event would trap less organic material, so the resulting fossil fuel deposits would be smaller and it would take much longer for a given amount of carbon to be buried.
Of course this is just one theory and there are many other factors in fossil fuel formation as well.
So anyway, since fungi and bacteria are more evolved today, it's unlikely that such massive buildup of organic matter would occur again. Any given burial event would trap less organic material, so the resulting fossil fuel deposits would be smaller and it would take much longer for a given amount of carbon to be buried.
Of course this is just one theory and there are many other factors in fossil fuel formation as well.
https://en.m.wikipedia.org/wiki/Carboniferous