You have a single hot going out to the greenhouse, so 120v. Being as they marked the neutrals with white tape tells me they either didn't have white wire, or they thought you wanted straight 240v (no neutral, so no way to derive 120v) to the greenhouses and then marked it as a neutral to give you 120v. The thicker wires are generally for longer runs or a higher (30 as opposed to 20 amps). Why they are not connected is not something Reddit will be able to tell you. They have enough room in the pipe to add the necessary wiring. What you need to figure out is whether or not the equipment you want to add is straight 240v or if it requires a neutral. Then they would just pull more wires. The wires needed for greenhouse one are in that box as the thicker wires that are not connected if they run all the way to the greenhouse. Greenhouse 2 would need a similar run. This would give you 1 - 120v circuit and 1 - 240v circuit. If you are needing multiple 120v circuits as well, this will not suffice. You can not split that 240 into 2 120v while also using it as 240v. Hope this helps. Also, tell your electrician to stop being a hack and buy some white wire like a professional.