The rules keep changing.
Imagine if, in our universe, the laws of physics kept changing. E=mc^2? Oh well today it's E=mc^3. Every physics formula is subject to change without warning. Basically everything might be fine tomorrow or maybe the universe will explode.
Turns out, magic is like that. It's energy drawn from a neighboring universe but the "neighboring universe" can shift from one to another at any time without warning and the new one may have completely different rules. The original magitek society was built during a time of unusual stability -- the rules for magic may well have been unchanged for thousands or millions of years and they didn't even know it could change. Until it did. When the shift occurred, the magitek devices drawing power (and, perhaps, a relative handful of sorcerers who were actively using magic when the shift occurred) experienced major malfunctions.
Magic may be in a state of constant flux at the moment. The rules could change daily. Sorcerers can still access the energy, probe it, and use it, perhaps not unlike tapping into a totally unknown power wire where you're not sure what the volts or amps are or if it's AC vs DC. First you find out, then you buffer some energy, then you use it. That's sorcerers. They have not figured out how to make Magitek items that robust. They need a steady, known supply. 227
If magic settles down again, Magitek could take off again. And nothing stops you from making a device today, based on today's rules, but you don't know if it will work for an hour, a week or a month, and if it fails, you don't know how spectacular that failure will be (maybe you can invent a "magic circuit breaker" to avoid catastrophe but the constant shifting of rules still means your device stops working and has to be redesigned to fit the new rules, which, again, keep shifting).
(To expand the electricity analogy, imagine trying to make a hair dryer that can work off of literally any power source. You can plug it into a USB port. Or a 120V US wall socket. Or a 240V wall socket. Or a wall socket in Japan. Or Germany. Or directly to the raw output of a nuclear power plant. It's probably possible but represents a big challenge and ultimately makes your hair dryer impractical -- you're spending more on the converters and buffers than on the device. This is what the people of this world face with magic. They can make the devices but since the properties of the power source keeps changing, the devices become something between impractical and dangerous. The sorcerers themselves might occasionally tap into the magic network and go "Woo! Wow. Okay. Not using magic today I guess. Check back later.") 284