People virtually never say “logarithm” in use though. They either say “log” or they say “lun” for natural log. Notice that both log and lun are one syllable, easy to pronounce etc.
Magnitude is an existing and important concept in maths - it would be extremely confusing to just overload it to mean something else.
The log of 3.1m is 6.5. How do you say "10^6.5"? I say "mag 6.5" and it is clear. The Richter scale famously uses "mag 6.5" exactly like this. If that was ever confusing, then we've managed to work past it, and this just expands the Richter scale to cover basically everything.
There's nothing particularly special about the Richter scale in that respect. All logarithmic scales (eg dB) work that way. Both the Richter scale and decibels (and other logarithmic scales) are also famous like other nonlinear scales[1] for being widely misunderstood so I'm not sure a lot of people would think your way is clearer than the current usage, which is just to say "3.1m" if that's what you mean. That said, I like log scales and logarithms in general so if you want to campaign for this scale, knock yourself out. I don't like that you're calling it magnitude though, because magnitude means a specific thing (the first coordinate of a vector in polar or spherical form).
Magnitude is an existing and important concept in maths - it would be extremely confusing to just overload it to mean something else.