It's not enough to "ensure that this country’s obligations were fulfilled and walk away", and it never has been [tenses changed]. This is exactly the problem, one that senior Leavers seem unable to properly admit to: you can't just leave without having some system in place that replaces all that EU membership entailed. The "transition period" is also necessary, as an interim arrangement.
The details need not be what May et al have set out to do, and I agree that the requirement to please everybody has wound up, as usual, doing the exact opposite. But this mess arises because implementing Brexit is complicated, and there is no way of avoiding this.
The sensible strategy was therefore either not to bother in the first place (going all the way back to before the referendum, I mean, rather than ignoring the result), or to admit that this could not be achieved quickly and to take the time required. Instead, everyone has tried to rush it through without knowing what "it" is. No wonder there's chaos.
Simply walking away was never an option, and never will be an option.