It's really pretty simple and not very controversial, Patrick. The bottom line is airplanes wear out. Each flight hour puts stress on the structure, the wings, the systems. Just like an old car, an old airplane gets to the point where the maintenance becomes unreasonable. And if you decide to buy new, why not buy a new model with new materials and capabilities instead of a decades-old design? The engines in the Mk 2 Buccaneer are Rolls-Royce Spey engines, a low-bypass engine originally designed for smaller airliners that RR customized for the Buccaneer. But RR doesn't manufacture that engine any more because it was too noisy for airliners and generated too much smoke in service at higher power. To replace it would require reworking almost all of the inside of the jet. That gets prohibitively expensive.
Works the same as for automobiles. After a while it's just time to get a newer vehicle and retire the old one(s).
That's not politics, it's mechanics. The politics comes in when you get to picking what to buy to replace it.