For most skiers and snowboarders, it's not a problem at all. If you're the type who keeps their helmet on from first chair to last run, you simply don't need a dedicated attachment point. Many riders never take their helmet off on the mountain, making this feature unnecessary.
The only downside is flexibility. If you do want to remove your helmet—during a lunch break, at a hut, or on a long uphill skin—you'll have to either stuff it inside your pack (which eats up a lot of valuable space) or just keep wearing it. There's no quick, clean way to clip it to the outside.
Bottom line: a pack without helmet carry is perfectly fine if you always ride with your helmet on. But if you regularly take yours off during the day, look for a pack with an external helmet net or clip instead.