Philco and Loctal Tubes

[Tom9589]

I've often wondered why Philco used loctal tubes in many of its sets during the 1950s.

I figured it had to be one of the following reasons:

1. Familiarity with using loctal tubes during WW2 in commo gear.
2. One of the engineers had a big concern that the non-loctal tubes would fall out of the sockets.
3. To get around some patent law.

Now, tell me what the real reason was for loctal tubes.