Conversation so far:
Where did Lowell Thomas begin Lowell Thomas's career?
broadcaster with the CBS Radio network.
What year was this?
1930.
What did he do for them?
delivering a nightly news and commentary program.
How long did this last?
After two years.
What was his next job?
switched to the NBC Radio network.
how long did this last?
1947.
Who did he work for?
CBS.
Why is this diffrent?
In contrast to today's practices, Thomas was not an employee of either NBC News or CBS News.
Who was in charge?
he was employed by the broadcast's sponsor Sunoco.

Question: Why did they move?
Self-contained rewrite: Why did Lowell Thomas move back to CBS?