I guess 75 ohm became more prevalent with the increase in interference sources...
At my parents we had a close & strong FM station that wreaked havoc with other FM signals and trying to get a distant VHF Channel 6 station that was right in line with that FM station. I knew the engineer for that strong FM station and he made us a custom notch filter to knock down his own station. :-)
75 ohm became more prevalent when cable TV became prevalent. Using 300 ohm twin-lead with cable TV would cause serious interference, both to the cable TV signal from external transmitters, and from the cable TV signal to external receivers.
Due to cable TV, houses started to be pre-wired with 75 ohm coax instead of twin-lead. I actually once lived in a house that was pre-wired with twin-lead, built in 1983...there was no cable TV in that area back then.
When TV manufacturers decided to offer cable-ready TVs that could be connected directly to the cable line with no converter needed—the input had to be a 75 ohm F connector.
For a while, probably from the mid 80s to the early 90s, TVs and VCRs were being made with 75 ohm F inputs for VHF/cable TV, and 300 ohm inputs for UHF. Then after that they did away with the 300 ohm input entirely and the 75 ohm F input was for VHF/cable TV/UHF.
Radio Shack (when there was a Radio Shack) used to sell a whole selection of signal splitters to deal with this. They had ones that took a 75 ohm input and split it out to 75 ohm VHF and 300 ohm UHF outputs.
They also sold signal combiners that took the 75 ohm VHF and 300 ohm UHF inputs and combined them on one 75 ohm output, so you could use an older VCR (with separate inputs) with a newer TV (with a single combined input).