Lubing
It a fitting doesn't have a grease zirk, than they are sealed, pre-lubed from the manufacturer, and require no lube maintenance. The theory behind them is that they are "sealed" and there is no way for the lube to leak out or dirt/dust to enter the joint (until they fail). There isn't much you can do with these other than wait for the part to fail and replace them with a piece that has a zirk.
IMO, the theory is flawed because all lubricants break down over time and use, therefore it just a matter of time before the part fails. Not much you can do to prevent this other than changing out the ball joint, tie rod end, idler arm, or whatever the fitting is.
This is just another plan by the parts manufacturer of "planned attrition". I once saw an episode of This Old House where Bob V visited Edison's house and the light bulbs he made back in the 30's were still in use and working in a light over the dining table. If that's the case, why can't GE make that bulb today? Why, simple they wouldn't make as much money selling a bulb that lasted 70 years, when they can sell you a bulb every six-months....