Absolutely baffled by your problems.

All services by Trenitalia are included in your pass, the only trains not included are a few very small private operators and Italo trains, which are a high speed provider in competition with Trenitalia Freccia high speed trains on the same routes.

I travelled from Siracuse (Sicily) to Bologna only last week and had no problems. Next month I will be travelling from Monaco to Venice without problems.

Granted all the Intercity and Freccia trains require separate reservations but they were easy to get and a max of 10 euro per train.

What trains did you want to take that weren't included? 

Yes, so why don’t travelers buy a ticket from their competitors with faster trains with cheaper prices.

I travelled from Milano to Verona 3 days ago. 
Ticket doesn’t included. Have to pay another 12Euro for the train.

from Venezia to Firenze. Only a few available time available to choose, 4 hours travelling, and have to exchange another train for twice. 

Turns out I buy another ticket for direct line, 2 hours time to travel. Easy and simple.

It seems you have confused the difference between buying a “retail ticket” and a Global Pass.

If you buy a “retail ticket” from a train company it includes both a ticket to travel and normally a reserved seat. 

With a Global Pass you have paid for the ability to travel on any train operated by Trenitalia without paying for the travel. However on many express and intercity trains the reservation is mandatory and there is a fee of between 3 and 10 euros (plus any booking fee) for each train.

Your “ticket” is your pass and the reservation is a separate document.

Most Express trains in Italy between most of the main cities are operated by Trenitalia, who also operate the majority of regional trains as well, which  can use your pass without any extra fees.

The competition for some express trains is operated by Italo, but they still charge a commercial fee for their services.

To get a cheap journey in most countries you have to pre-purchase your ticket for a specific train and they are non-refundable if you miss that train for any reason, Unlike a Global pass where you can take any train (with a reservation) i.e. fully flexible.

In much of Europe fully flexible and on the day prices are significantly higher, often double or triple the saver fares so Global Passes come into their own.

12€ is the reservation if you book via eurail.com, not a new ticket. It is clear on the website of eurail.com that some trains require a reservation. A normal Ticket would cost way more. 

You can reserve a seat also at the ticketoffice of Trenitalia or online via ÖBB for 10€.

Probably you should do your homework before complaining…