Perhaps a better analogy: let's say you're hiring people with the offer that you'll pay them $2M the first year, then nothing for 20 years. The danger is that the person will quit. So it is more conservative to offer a deal where you pay them nothing for 20 years, then $2M. Then you're pretty sure they'll stay, especially if they're 15 years in.

I think that's probably the best way to understand the salary/pension trade-off. The public sector is geared to be quite risk averse in investments, so it offers back-weighted comp to try to be frugal on training and provide continuity.

There's also basically no other employer that can credibly offer this kind of comp, so the public sector, by offering it, can compete quite well for talent in the space of those interested in that configuration. It's not the only way to run things, but it makes some sense.