1 - you're not allowed to hand fly in RVSM airspace which is where we spend 90% of our lives
2 - hand flying a big jet when it's a beautiful, low workload, CAVOK day = a lot of fun, but it's a completely different skill to hand flying it when it's sh!t weather IMC to minimas and you're dealing with multiple failures and associated checklists - which is the most likely scenario as to when you'll actually "need" to do it.
3 - it would be extremely prejudicial to safety to do hand flying on the line for the sake of realistic "practice" when it's sh!t weather and high workload, let alone with real live failures
4 - I don't know about boeings, but any failure mode in an airbus that knocks out both autopilots, also puts you in alternate or direct law, which is a very different flying "feel" to normal law, and certainly something you couldn't and wouldn't want to practice on the line if you valued your job
5 - I'm all in favour of more, non-assessable sim sessions, to relax and practice keeping the instrument scan current and the hand flying skills we DO need to keep the blue side up in non normal high workload situations, but lets keep it in the sim. Truth is that total autopilot failure in a big jet is a very very remote possibility and a pretty serious situation (because it's 99.99% of the time associated with failure of multiple other systems) and should be treated with the respect it deserves like any other emergency.
6. I don't see people on here agitating to practice, in the aircraft, any of the other handling related skills that we all wish we were more current on - like emergency decompressions or GPWS climbs - but the probability of encountering one of those is actually much much more likely than spending an extended period hand flying due to total automatics failure. I can't see what the big deal is myself.