Yes, that's right - now you need to get permission to climb to the very top of Teide, otherwise you can reach only the top station of the cable car. But there is still a third option - to get (in any way: by cable car or on foot) to the Altavista Refuge, spend the night there and in the morning at dawn (until 8-9 am) climb the trail to the top of Teide without any permission. A night at the Refuge of course should be booked in advance.

This is quite convenient, a description of our climbing including a little about the refuge you can see here.

I think the permits came from the fact that since then many more people began to climb there. As with many natural places, the state of which, due to the increased popularity, has to be monitored more closely.