For a player like Dallin Hall, and any player like him (starter on a good team in top conference), what is the motivation of entering the portal?

NIL. Money matters, but it's likely that a player will get similar money elsewhere in a lateral move. The case could be made that by staying in place, more opportunities are created as a result of networking and relationship building.

Style and role. Due to the portal creating so much roster uncertainty...how can a coach forecast a player's role amid the chaos? Even style of play may have to change to match whatever the roster ends up allowing.

Coach. Coach gets fired or leaves. New coach doesn't value you or brings his own player(s). This one makes sense.

The portal has gone too far. It's hard to be a fan when every player is a free agent and your entire team can disappear. I'd like to see a 2 transfer rule, with a bonus transfer being awarded if a coaching change is made. There is not enough continuity. Same goes for coaches. Coaches should be incentivized by NCAA to stay put. Meaningful bonus from NCAA for hitting 5 and 10 year marks. This will be good for players as well and reduce their desire to transfer as often.