easy answer - putin won't negotiate until he achieves his...

easy answer
- putin won't negotiate until he achieves his objectives

and
Ukraine want their territories back .....NEITHER side are willing to negotiate presently,
and there is miles between them in expectations

the other issue is TRUST .....Ukraine wants a permanent solution where they are gauranteed safety ....and not putin coming back when he has re-armed .
signing a bit of papaerr can never be enough for Ukraine because they don't trust putin to honour it