TTL (chiefly in the form of the 7400 series of IC's) became an early standard for compatibility in commercial electronics during the 1960's and 70's. It used a low supply voltage (5v), and set V levels for binary low and high.
Soon there were the inevitable advances (Schottky, Low power Schottky, H, F, etc.).
It became common to print tables comparing their characteristics against TTL, showing why they were a better choice than TTL.
It wasn't long before the tables had several columns, one for each family of IC.
And even though the more modern series use less power, and perform better, TTL was never dropped from the first column.