The reason is, well aside from entitlement issues...
The electric meter may not cooperate. Meters are not necessarily designed to detect current flow bidirectionally. The old ones' discs may spin backwards, but that doesn't mean their digits will roll backwards - they may have a ratchet to disallow that. Smart meters aren't designed to, or are designed to not to. The newest meters can turn that function on, but only if the power company commands it remotely.
So, if you push 1000W onto the grid for 8 hours, you expect your electric bill to be 8 KWH less... actually, it will be 8 KWH more, because the meter has no idea you were the source of that. Whoops!
Any backfeeding onto the grid will require the assent of the power company, so they can fit a more sophisticated meter.
So in a rental, it isn't going to happen.
"But my solar won't exceed my usage, so my meter won't roll backwards". Nope, that fails too. The problem is, the meter only cares about your instantaneous usage vs generation. Your solar panel might make 500W consistently all day. However, your house's load jumps all over the place! Usage is intermittent - when you turn on a light, or when a heater or dehumidifier cycles on. The only constant load is the "vampire loads" from TV, cable box, computer, wall charger blocks, etc. which might amount to 30 watts at most.
So you need to expect that your meter will be needing to roll backwards, a lot. There are gadgets that can throttle the solar generation so that it never rolls the meter backwards, but they need to be hard-wired, so we're back to your landlord's permission.
If you want to support green power, buy into a co-op solar installation. If you want power when the AC grid is down, grid-tied solar is incapable of that, so that's the wrong tech anyway. You need a battery/inverter solution, which can be augmented with portable solar.