RE: Hoses vs metal high pressure hydraulic lines.
Two reasons.  Hoses can and do deteriorate over time, even the best of
them.  And hoses flex under pressure absorbing/using some of the pressure in
the system.  And they flex even more as they deteriorate, get softer.
Example: Those wanting best brake performance (especially under hard use)
use braided metal lines   for the short sections of brake line at the wheel
where rubber hoses are the norm.  Long hoses just magnify these effect.
Plus a failure of a hose is usually complete causing complete failure of the
system.  Failure of metal (rusted or corroded) metal lines will usually be
smaller, causing leaks but not a catastrophic sudden failure.