On the nuances of Moonbeam and similar spells

So I recently watched the latest Dungeon Dudes video going over commonly misunderstood spells. One of them was Moonbeam and other spells that take effect “When a creature enters the spell's area for the first time on a turn or starts its turn there” (DnD Beyond entry for Moonbeam). In the video they state that this does not include the moment the spell is cast and when the spell’s area of effect is moved during later turns. Instead, in these cases the effect is triggered at the start of the affected creature’s turn. I found this quite strange as the spell’s description never specified this. However they direct the viewers to page 16 of the sage advice compendium where this is elaborated upon. It’s is stated that the intent of such spells is to set up later effects as opposed to impose immediate ones. So a creature is considered to have entered the spells area when they move or are moved into it but not when the area moves onto them. But they are considered to have entered the area once their turn starts. Aside from me finding this to be poor wording in the spell descriptions I find it to be simply illogical. How can a creature be in the center of a Moonbeam but not enter it until their turn starts? In other words I can be within the area of effect of a spell but not have entered it at the same time. Is there something I’m missing here? Or do I just need to suck it up and move on?