There's no such thing as a simple repair on a current Apple device. They're simply not built to be very field-serviceable, because Apple's customers would rather have a thinner or lighter device than one that's easier to repair. Open up anything in their current line and you'll find fragile ribbon cables, delicate connectors, wafer-thin pieces of glass and fragile things glued to other fragile things. Ifixit's guides are peppered with warnings about things that can be broken with slightly too much force or by prying in the wrong place.

From Apple's perspective, amateur repairs are potentially a source of serious damage to their brand. The effects of inept repair are likely to reflect at least as badly on Apple as they do on the repairer. One bad third-party battery could be enough to trigger a global media shitstorm, in spite of it being nothing to do with Apple. Their customers don't expect iDevices to be user-serviceable, so raising the barriers to entry for repairers is a clear win for Apple.