Why FT8 uses a set of well-known dial frequencies by band, and on 20 meters that is 14.074 MHz USB. Because each FT8 signal occupies only about 50 Hz and stations spread out across the 3 kHz audio passband, the actual occupied spectrum runs from roughly 14.074 to 14.077 MHz. Sticking to these standard watering holes is what makes the mode work, since everyone must be listening in the same slice to decode each other.
Watch out The 14.110 to 14.113 MHz range is in the digital/data region but is not the FT8 calling segment; historically that area saw other data and automatic operations. FT8 lives in the data segment near the bottom of the band, not in the CW or phone portions.
20 meter FT8: dial 14.074, signals spread to 14.077. Remember 074 and add 3 kHz.