I take your point but there are downsides to restricting oneself to only Roman letters. In a few fields I've been a student of, there's a bias against introduci

I take your point but there are downsides to restricting oneself to only Roman letters. In a few fields I've been a student of, there's a bias against introducing Greek letters. The downside is one does run out of letters. Eventually one needs Greek letters if one wants to not communicate in an amateurish manner -- either that, or one is forced to use multi-letter variables like "Eff", "Density", which are somewhat unwieldy, especially in complex expressions. Also some Greek letters have such a strong conventional association with certain quantities that using Roman letters in their place can be more obfuscating, e.g. ρ = density, Δ = change, η = efficiency, θ = parameter, σ = standard deviation, μ = mean, τ = time constant, etc. Notation is to some extent a function of a community's conventions.