Euler thought up or improved way too many things for them all to be named after him, it would get too confusing.

From his wiki: "Euler's work averages 800 pages a year from 1725 to 1783. He also wrote over 4500 letters and hundreds of manuscripts. It has been estimated that Leonhard Euler was the author of a quarter of the combined output in mathematics, physics, mechanics, astronomy, and navigation in the 18th century." https://en.m.wikipedia.org/wiki/Leonhard_Euler

And a relevant xkcd:

I guess Euler-Langrangian mechanics was too much of a mouthful!

An old bit of wisdom: "Most scientific concepts are named after the second person to discover them"

hmmm... I was going to go with continuum mechanics as that seems made up. Maybe Euler contributed something to Lagrange.