I think jr pretty much covered it.
But, not resisting the urge to be pedantic
; the ions are not from material off the surface of the cathode. They are produced from the residual gas in the CRT. It's impossible to achieve a perfect vacuum. The majority of the ions are produced when the electron beam hits a gas molecule. Some may be produced by the heat of the cathode.
Ions are bent in a magnetic field. Just not much. The force acting on them is the same as for an electron of the same velocity, but they have many thousand times the mass of an electron and are thus deflected less.
Electroluminescent has a different meaning than would be used in a CRT, even though the same material may be used. I don't completely agree with the wikipedia definition either. Most sources define it as a phosphor being excited by an alternating electric field or current.
Pumping speed can only buy you so much. The RF induction heating that was mentioned is an important element. Even in a very high vacuum the materials used in a CRT will only outgas at a certain rate unless they are heating to help drive off the gasses. The heating cycle of the envelope is important also.
Which translate to time and money. CRT manufacturers don't want a product to die so quickly that they get a bad name, but they could probably care less whether it dies in 5 years or 50 years of use.
The getter flash helps them to minimize how well they have to outgas the CRT.
This guy avoids having to due a getter flash for a vacuum tube by seriously degassing the tube before sealing it.
http://paillard.claude.free.fr/
O.K. I'll be quiet...
John