Passport weighs 2,000# more PER engine, it’s a high altitude, Mach .90, low cycle design when a RJ needs a lightweight, low-ish altitude, M.78, high cycle engine. Try again.
Engine mass is not a linear function of thrust. The Passport was designed for a very specific application. Now could some of that technology be used in a new RJ-specific design? Sure, if an OEM has a business case for a new RJ, which doesn’t exist now due to poor sales.
I think we can see why the CF-34 lasted as long as it did. Designed to lift the A-10 with its bathtub cockpit and lots of fuel for low loiter missions, it meshed pretty well with the need for a RJ engine. Passport is for the high flying bizjet segment, not so great a match.
The weight increase eats away engine fuel efficiency gains.
The key thing to realize is that the engine weight gains are what provides the fuel efficiency gains. To get better fuel burn you need bigger fans which means bigger/heavier fan and nacelle, and higher temperatures and pressures inside the engines mean heavier blades with more complex shapes, heavier bearings and rotors, etc.
The trend has been really clear if you've followed jet engine development. Unfortunately the trend is not improving. We keep getting better fuel economy and other important gains such as lower noise and other emissions, but the cost of this is more weight and more cost. Some new materials like CFRP fan blades and CMC turbine parts have been developed, but these have cost a lot to develop and still cost a lot to produce.
The pilots think they gave up too much in the earlier scope clauses. Now we see the way tech has developed since then has closed the window. CF-34 era engines do not provide enough fuel efficiency to be economical and can't provide the payload/range that airlines desire. Fixing those problems can only be done by heavier engines, but these bust scope. Vendors felt rational adjustments would be made with both sides giving up some things to allow the heavier aircraft into service, but no one involved is behaving rationally. Pilots are upset about all the jobs they've given away to RJs, airlines are used to finding some way to get the pilots to knuckle under.
Welcome to the real world.