For the "they" of your provider, who is held accountable for allowing abusive traffic, the goal is to provide you outbound connectivity but to do that they also need to ensure they don't get de-peered or their network ranges blocked for hosting abusive traffic. Even for things which don't transit a 4th party there is negative incentive to let your customers abuse each other just because the addresses are reachable. This almost always results in automated systems with limited incentive for good uses of port scanning to be allowed.
For the "they" of the end system is (most likely) they didn't make the entire system available to you, just some select services for use in a certain way (e.g. loading their website). Doing that does not provide them an obligation to continuously allow all traffic received at the address to be processed and it's very likely they'll just block you entirely as another layer of defense.
How is this different from scraping publicly available websites? i.e. why would you get in trouble for one, but not the other?
Big companies with deep pockets will even bankrupt other companies this way. For an example, look at how Sony sued playstation emulator companies over the most bullshit claims possible, got an injunction, killed their profits and then it didn't matter that they lost in court afterwards. In my country, the judge would have estimated the profits the smaller player lost as a result of Sony's frivolous lawsuit and forced them to pay it all back on top of the legal fees.
In short, who's getting put out of business for redisplay or derived data uses of publicly available data?
Stealing someone's bitcoin? It's just network connections. Logging in to some admin portal with default passwords? It's just network connections.
> Why would they make a computer accessible to me if they don't want me connecting to it?
Why would they write bugs in software if they don't want to write bugs?
The administrator of the network didn't intend to allow port scanning, but there were no technical measures (firewalls) to prevent it, and you did port scanning => you're wrong.
The writer of the access control software intended to have no bugs, but a bug slipped in to allow you to exploit it => you're wrong.
I just want to know what's out there.
> exploit
How is this exploitation in any way?