Desilu was producing both The Lucy Show and You Don't Say! at the time.
I had forgotten
You Don't Say! — thank you for the correction.
Still, that was an inexpensive gameshow made for daytime television.
Star Trek and
Mission: Impossible were worlds apart from that program
—and
The Lucy Show, for that matter
—in terms of the scale and expense of the production. And for the previous two broadcast seasons (1964-65, 1965-66) Desilu had no one hour dramas on the air.
Star Trek was a pretty ambitious project at the time, so any uncertainty NBC may have had is understandable. As far as CBS, it's been often reported that CBS was already developing Lost In Space when Star Trek was pitched to them and it was a case of the early bird getting the worm.
Gene first made that claim in
The Making of Star Trek (1968) and it's been repeated in many other places since. According to production documents cited in two different Irwin Allen books published in the past 3-4 years, however, it's not true. Allen and his partners didn't pitch
Lost in Space to CBS and the network didn't buy the show until well after Roddenberry's disastrous pitch meeting for
Star Trek.
I brought up CBS in the context of
Mission: Impossible, though, not
Lost in Space. Because of
Star Trek's longevity,
Mission tends to get sidelined in this history, but it's important to remember that
Mission was equally as ambitious and expensive as
Star Trek (day-to-day, it was actually
more expensive to produce than
Star Trek). The objections of some Desilu board members were as much about that show going forward as they were about
Star Trek.