Quality of life, I don't want to wait for an animation to play for my druid to shift out of animal form, climb the ladder then shift back. It also creates new logical problems. If my character can briefly shift out and back into form to climb a ladder why can't she do the same to cast a spell or use an item? Having animals climb in animal form is the quickest easiest solution.
This is rigid naysay thinking. You don't want to wait all of two seconds for an animation to play (an animation that could be sped up for this purpose and even be played while moving)...while likely still having to wait for longer than that in queue for your turn to climb the ladder anyway? If the Druid moves first (and animation grounded you for a second), the companions behind could easily be made to climb ahead/skip turn. No/very little time would be lost in practice.
So you consider the breaking of physics itself to be less of a logical problem than taking slight liberties with some small specific D&D rules for quality of life purposes? Wowsies. Larian has already taken more liberties with their implementation of wild shape, I don't see you complaining about this. You can easily go from one shape to another in combat, DISMISSING a shape is now FREE, and changing in combat is a bonus action instead of D&D RAW full-action. And how is this much different from dismissing a shape during climbing ladders (and regaining it immediately after)? Besides, if you listened to the D&D rep on the panel of hell stream, he explained the reasons for limiting number of wild shapes are that tabletop D&D Druids have virtually unlimited selection of wild shapes that potentially could break encounters. This is not the case where Larian controls every encounter. A very quick change could be explained/roleplayed however you want...changing back to natural form for a short time and your body still is in flux for instance.