it's the exact opposite.

It's actually much harder to replace glass itself than to slap a new assembly on.

If somebody comes in with a completely shattered glass the glass panel might be cheap but the labor involved to remove every single tiny piece of glass is what drives the cost up. When you're billed this is how the price is calculated.

Typically replacing the entire LCD assembly would cost you $45-135 and about an hour on any given phone. Price is determined by availability of replacement parts.

Replacing the the glass panel only, costs the glass itself , and the 2-4 intensive hours of labor required to completely remove said glass and to make sure no leftovers are found otherwise when putting the new one in would crack the digitizer and LCD underneath..

For these types of jobs the labor itself costs more than the parts themselves.