It's not so much raw sites as it is the online manga sites. Some of these chapters appear in magazines and some don't, but all get split into partial chapters for the free manga sites. The raw sites just steal from them and translators scanlate those raws; You're not going to change the Japanese free online model or get the bot driven raw provider to change so the easiest solution is for scanlators to wait to release full chapter rather partial.
I kind of agree, the partial chapters end abruptly at awkward points so you're forced to reread with each release. It's not hard for scanlators to either scan all at once (same effort just all at once rather than bit by bit) or upload at once (opposite, bit by bit) and it saves a little effort since you would only upload once. Either way, it's just someone else's preference so whether they listen or not is up to them.