Because PNG is not scalable and looks ugly.
The actual SVG was generated using https://viereck.ch/latex-to-svg/ from
the following LaTeX code:
\lambda\kern -.1667em\lower -.5ex\hbox{$a$}\kern -.1000em\lower .2ex\hbox{$\mathcal M$}\kern -.1000em\lower -.5ex\hbox{$a$}
Signed-off-by: Kakadu <Kakadu@pm.me>