Why is the Sun's Luminosity not equal to the Zero Point Luminosity?
The zero point luminosity L0 is the luminosity of a star whose absolute bolometric magnitude Mbol is 0.
IAU recommends the value
L0 = 3.0128 &times; 1028 W.
If the Sun's Mbol is +4.74, then
L0 / Lsun = 104.74 / 2.5 = 78.7,
which is consistent with Lsun = 3.828 &times; 1026 W.

Your understanding that Lsun &equiv; L&#9737; is correct.
Maybe there was an accidental substitution of L&#9737; for L0 at some point.
Curiously, the number 3.75 &times; 1028 appears in the Wikipedia:Sun sidebar as the Sun's luminous flux in lumens, a quantity more applicable to a light bulb than to a star.