Because range voting devolves to approval voting. Why rate a candidate 4/10 if you don't want them to win? You insincerely rate them 0/10. Why rate a candidate 8/10 if you want them to win? You insincerely bump them to 10/10.

On top of that, you then have to consider the potentially lower popularity of your favourite choice against that of the current lead contenders. Do you reduce your vote for the better of two evils so that your sincere preference has a better chance? Ugh.

I'm not trying to suggest tactical voting doesn't exist in other systems, but to suggest that it doesn't in Range voting is either misinformed or disingenuous.