Even 20 years ago, when I was programming an independent TV station, syndicators were coming to us early, with only 60-ish shows produced but a commitment from the network to do two more seasons, with those to be immediately offered to syndication as the season following began.
Even with that commitment, the station that buys the syndication is risking burnout of the first batch of episodes. If you're playing a half-hour sitcom once a day on weekdays, and have 66 episodes to work with, each one (save one) will be played four times during that year. Yeah, 22 more episodes will arrive the following September or October, but they're aired in a month and you're still playing the 66 you burned the season before.
100 shows used to be achievable in five seasons. Increasingly, seasons are shortening to 13, 10 or even eight episodes, making 100 a hard number to hit while the show is still fresh.