It will take a lot longer than an hour and a half to get from Paris to Venezia by flying. The plane might get from one runway to another in that time, but the total travelling time for a passenger from city to city is unlikely to be less than four hours.
I agree that I wouldn't want to spend ten hours sitting on a train. I'd do a journey of that length overnight, asleep in bed, or I'd break the journey to visit somewhere interesting en-route.

"I have long since forgotten about the 'charm' of sitting 10+ hours on a train, when you could be flying for 1 1/2 hours at half the cost."

Well, compared to the "charm" of schlepping back and forth to airports and standing in check-in and security lines followed by being shoehorned into high-density seating followed by standing in luggage (and maybe customs/immigration lines), sipping a flagon of 1664 while watching the French countryside flash by does have a certain appeal.

I willingly pay extra for the privelege.