Apples to Oranges
Exxon works in a market that the price of their ONLY input (crude oil) is determined by collusion (OPEC). OPEC's goal is to control the extraction of oil to maintain a price per barrel to maximize profits for it's members while balancing pressures from governments and markets as well as elasticity of consumer demand. The cost of the input is artificially high (reduced profit) because of OPEC. They also have costs that deal with capital gains, pollution mitigation, taxes, education, R&D, refinement, insurance, employees, legal team, lobbyist, legacy costs, $507.5 Million in punitive damages from the Valdez spill (92 Million outstanding), maintaining / upgrading massive facilities and infrastructure, etc. They are an ENTIRELY different beast than the underground cannabis cultivation industry.
If only Exxon raised their price to $80 a gallon they would go out of business. There would still be the other refiners / sellers offering $3/gallon gasoline and nobody would buy $80/gallon gasoline from Exxon sellers.
If gasoline were arbitrarily set BY ALL SELLERS at $80 a gallon CET PAR than consumption would drop drastically. So much so that the percentage change in consumption would be greater than the percentage change in price leading Exxon to less total revenue and lower profit. Price is higher than equalibrium so there would be an excess of quantity supplied and fewer quantity demanded. That "excess supply" would cause the price to drop as sellers aim to see greater profit by undercutting their competitors to see increased total sales. This would happen until the market was back in equilibrium.
Cannabis has production costs (dirt / water / fets / lights / pots / seed / time) and a risk premium (worry / incarceration / fines) which is subjective based on the individual as they evaluate their individual risk of getting caught. Most transactions are black market and hence not subject to laws. They are not paying taxes, subjected to legal ramifications, or subjected to labor laws. These are things that legal enterprises like Exxon have to deal with. The price of cannabis must exceed production + risk. If the price is higher than the cost an individual can produce cannabis in their eyes; they as rational people will enter the market with profit as their motivator and start growing. People will continue to enter the market until it is "saturated" and the firm realizes a "normal profit." Most legal agricultural farmers fall into the category of "normal profit" which is why the US government subsidizes farmers not only with money; but the dumping of product domestically through intentional disposal / spoilage and internationally via foreign aid.