I would've thought cruise ships would be paying already to dock and offload their passengers. If not then it seems a no brainer that they should.
Of course they do. Any port charges berthing fees. Every port is different regarding their charging structure- some charge by the hour and the passenger count, some charge a flat fee by length and some a combination of the two.
But the fee is always substantial. In the case of Amsterdam the reason why many ships moved to Rotterdam was more complex than the city visitor charge (separate from the port fee). Part of it was that visitor charge, part of it was the lockage and pilotage fees (Rotterdam of course has no locks to navigate) and part was the degradation of Passenger Terminal Amsterdam- Rotterdam being a far superior passenger terminal.
It would not surprise me if Venice Port lost 4,000 jobs- partly through port employees and partly through the supply chain for food and beverage, bunkers etc. However the port of Venice still employs almost 22,000 employees for the ferry traffic and the large freight ship traffic as well as the fishing industry (the latter mainly at Chioggia).
Cruise ships were never banned from Venice- what was stopped was ships over 2,000 pax capacity using the Grand Canal (which they apparently had to, for the old cruise terminal).
It is hard to find out the size and draught limits for Venice, but Venice still has two working cruise terminals on the mainland- at the ferry port of Fusina and the freight port of Marghera. I suspect that most cruise lines voluntarily moved to Ravenna and Trieste (rather than use the other Venice Terminals) due to lower berthing fees and the opportunity to add to their profits by charging for the 2 or 3 hour bus ride from those ports to Venice.
In the same way as they boost their profits by charging at Zeebrugge for the bus to Blankenberge, pretending that Zeebrugge Rail Station doesn't exist.
This forum does very little to explain to cruise ship passengers what there is to do at Ravenna and Trieste (in the way it does for Le Havre or Warnemunde/Rostock- where it rightly tries to dissuade people from the similar length bus rides to Paris and Berlin respectively). Personally if I landed at either of Ravenna or Trieste there is no way I would travel to Venice- by excursion or independently.
Likewise if I arrived at Chioggia on a cruise I would concentrate my day on Chioggia and the Lido, not central Venice- supporting their economies using the integrated boat and bus service, and exploring the town of Chioggia.