Why is LC39A's TEL enclosed, but the newer SLC40 TEL is not?

Question

After the AMOS-6 explosion on the pad at SLC-40 in September 2015, SpaceX spent a lot of time rebuilding SLC-40, including a very big update on the TEL (Transporter/Erector/Launcher). Whenever they speak of it (Gwynne Shotwell or on the CRS-13 launch webcast) they mention that the original TEL was built before they ever launched a Falcon 9, and they have since built Vandenberg's SLC-4E, and LC-39A.

Thus they have a lot of experience now on how a TEL should be built.

When they revealed the LC-39A TEL it was very different from the previous looks and was mostly enclosed. But on the CRS-13 launch it because clear that the newest TEL was still a lattice design.

Initially I was wondering why they did not enclose it, but perhaps a better question might be, why was the LC-39A TEL enclosed?

Answer 1

The LC-39A TEL is also internally a lattice, just has panels attached to protect it from rocket exhaust.

Unfortunately I can't find the links now, but I recall that there were pictures of LC-39A TEL in the few months/weeks before its first launch, and it lacked the protective panels. They were only attached at the last moment.

We also know that SpaceX continues to iterate on their TEL&GSE. They attached some of the Falcon Heavy hold-down clamps and tail service masts in between Falcon 9 launches.

Therefore, my best guess is that they simply haven't done it yet. They already slated CRS-13 to launch from LC-40, and the panels aren't necessary, so they skipped that part to launch sooner.

Alternative guess: LC-39A was designed for Falcon Heavy which has higher thrust, so that TEL needs additional protection.