Some thoughts...   In the late 60s, early 70s the number glass tty's being made were actually fairly small at first.  They tended to be custom build for specific uses, such as the airlines or wall street traders.   The idea of the glass tty was not quite ready to be birthed.   Mostly because the cost was high and the need was not quite yet there.  IIRC VT05 and the like cost multiple thousands of dollars in late 1960/early 1970s money [FYI - the website says that's between $13K-$15K in todays money].

Remember that at the time the of the VT05, its follow on the VT52 and its contemporary, the logic was built primarily with using MSI TTL; including all the video logic to drive the display itself.   A dominate cost of the terminal was the static ram chips.   A single 24x80 lines of 2000 chars was $50-100 in OEM quantities.  The keyboard cost about the same.   The video sub systems were black and white TV monitors.   You still need a case, keyboard and the rest of the logic.     The $999 cost of the Lear Siegler Kit that you assembled yourself was a steal.    DEC used an Intel 8080 in the VT-100 a few years later, they paid approx a huge amount of money for it, but they were able to make the logic board so much smaller.   IIRC the original price for the VT-100 was $3500 in 1976 (they did sell a ton of the them).      Shortly thereafter, most terminals had 8080's, 6502s, or Z80s in them.    Motorola built the first video chips and it's interesting, how many of the terminals all used same video chips but the processors were more varied.   With the prices settling around $700-$1.5K mark by the early 1980s.