Because they've been rolled into the daily event objectives for well over a year and can acquire up to 4 per day. For the average player that wants to get a good night's sleep this is significantly better than forcing yourself to log in every 4 hours. The crystal descriptive text could do with some updating.
You haven't been getting 4 hour crystals for well over a year now.
What was the 4-hour crystal has for a long time been the "free crystal" which comes in the DSE and has since like November of 24.
