A key material was lost Building on @Andon's answer: The ability to aquire or manipulate any material upon which the tech is dependent is lost in the Fall. Be it antimatter, "duranium", or any other form of unobtainium. As @AngelPray suggests in his/her comment, this forces present-day people to scavange pre-Fall equipment for material or puts a lot of power in the planets or facilities that can produce the element. For example, planets that were the source for this material may have been destroyed in the Fall or the records to locate them lost. Smelting or other processing might have been concentrated in a couple of systems and were destroyed. This leaves a precious few places to get the materials and only a few places that can process it.
A key transportation technology was lost People can still get around in smaller ships, but the tech to build the big super-tanker/freight ships is gone. "Mass produced" on a galactic scale is breath-taking. Consider for a moment just how many tons of wheat is needed to feed one good sized city for only one day. According to the USDA, the average U.S. citizen ate 132.5# of wheat annually in 2011. That doesn't sound like much, only a bit more than 1/3# per day. BUT, the population of LA in 2011 was 3.8 million people. That was 1.38 MILLION pounds of wheat DAILY. Generally, a semi-trailer can haul 55,000#, so we're talking just 25 truckloads a day (people who know about shipping are wondering at that cavelier statement). Now let's assume something stops diesel semi-tractors from working and all we have to work with are 1/2-ton pickups. Suddenly we need 1,380 truckloads, plus drivers, plus the congestion it causes, plus the hassle of loading and unloading.... The loss of those interstellar super-freighters all but shut down the ability to transport the mass-produced products to all the worlds, leaving access to parts and products in the hands of a few entrepenuers who can handle the load for people who can pay the prices.
The economy is in ruins Back in 2014 there was a shortage of .22 calibre ammunition. There were a lot of reasons for the shortage, but the point I'm making is, why didn't somebody take advantage of the higher prices to fire up another plant? Wouldn't they have made their money back? The simple answer to a complicated problem is "no." The cost of building an entire new manufacturing facility is really, really, really high. So, if your means of mass production was destroyed during the Fall, you can't just bang it all back together. Just the cost of cleaning up the rubble is prohibitive. Look how long it took to clean up Europe after WWII. This is likely the easiest reason why you don't have access to the mass-produced items anymore. The factories and manufacturing plants are gone, and no one can afford to rebuild them yet. This leaves small manufacturing facilities with severely limited distribution.
Employee shortages And that assumes that you still have the people to staff those centers. I assume people died in the Fall. Most planets will be desperate to keep employees in jobs that feed, house, and protect local populations. Who cares if anybody wants an intragalactic radio? Breakfast is much more important! The government might spare a handful of people to build/repair the toys congressmen depend on to look important... but only that handful can be spared!
When trade is cheap, information is power. When trade is expensive, trade is power. Massive ruination like the Fall inevitably shifts power. Beforehand, most of the power was probably in the hands of interstellar corporations... but those corporatations were gutted during the fall. Most were destroyed as symbols of tyranny and the rest were annexed by local governments as critical resources to protect local economies. This distributes the power massively, and now the little guy once again has the ability to exert his/her influence! With the big corporations gone (and, more importantly, their legal departments gone with them), small mom-and-pop shops building and selling cool tech are popping up all over the place. They can't produce anywhere near what the big corps could... but what they produce is amazing! Because innovation didn't die with the Fall. If anything, necessity breeds invention, and the Fall is actually responsible for thousands of wonderous new products ... that almost no one can obtain 'cause there's only so much stuff you can fit in the back of a proverbial 1/2-ton trade ship.