Have you ever seen a tech company calling a 65y.o. retired wizard to debug a system failure? I doubt it.
In manufacturing it so regular, that typically senior technical people retire as soon as possible to form their consulting firms and charge much higher rates, just by selling their multi-decade expertise back to their company.
In oil & gas, there are consulting firms that their role is to just store and provide domain knowledge to companies who lost their experts.
In tech, consulting firms provide cheap labor.