Scannerless parser grammars, especially with GLR, are extremely flexible and a pleasure to write. They are the "DWIM" of parsers. But you pay a high price in performance for that flexibility.
Since programming language grammars don't tend to change much, by the time you have a production compiler it's usually worth your time to switch to a split lexer/scanner in order to get that extra performance.
Scannerless parser grammars, especially with GLR, are extremely flexible and a pleasure to write. They are the "DWIM" of parsers. But you pay a high price in performance for that flexibility.
Since programming language grammars don't tend to change much, by the time you have a production compiler it's usually worth your time to switch to a split lexer/scanner in order to get that extra performance.