Why do 1st Century Roman groups avoid combat

[Olaf]

Though the fight in that video might have looked specatcular to the spectators, I would hardly call it a "battle demonstration".
Coming from the Gladiatorial crowd I know how much training, disciplin and trust in the fighting partner is needed to show even remotely plausible combat moves with Roman and other antique weapons.
Of course having sturdy helmets that protect the head, face, neck as well as manicae for the unshielded arm does help a lot in doing freefight displays with a good amount of safty.
In the video you can see very well that the Romans do not stap with the point of their Gladii and the Dacii do not chop very hard with their weapons.
But these kind of battle displays only afirm the typical blade on blade fencing and shield pushing we now and "love" from Movies and TV.

With longer blades and more sturdy armor it is much easier to find a basis were even people that have never practised together can have safe and even competitive free fights.
But even in these systems like the GErman Codex Belli or the so called International rules attacks to the hands as well as the head are banned and stabs may only be performed by spears and only in a downward thrust targeting below the chest.
All free fighter I know use differnet kinds of padded or thick leather gloves to protect the fingers which might not be historical but look fitting with the early medieval gear. In a Roman environment manicae with added protection for the fingers would have to be manditory.
Lastly most freefighters use extra sturdy helmets and shield buckles and I have seen a blunt Gladius stab right through the thin brass Umbone used on a Deepeeka Scutum once.
So you are basicaly looking at getting a second set of gear just for doing reasonably safe free fighting displays in addition to a lot more free time spent training to be a safe fighter yourselve.