Before the Roman collapse in Britain around 410, the island had bankers, public baths, factories, and elaborate public infrastructure. In the England of 810, they were working hard on unlocking the "towns" tech, and largely failing. No one intentionally went around destroying technical know-how, but the ensuing 400 years had left people so much concerned with other, more immediate problems that the skills and industrial infrastructure of Rome had atrophied into near-nothingness.
Now transpose this to a situation in which Rome did not slowly recede from the provinces over a century or two, but simply stopped one morning. Also, your planet was never designed for human habitation. Also, anything you possibly need for survival must now be built on your planet, using manufactories you do not presently have, and skills and personnel who are not present on your world. And your government has just collapsed because the entire planetary population is freaking out.
Modern high-tech life is the infinitely narrow tip of a giant iceberg of trade, production, social compacts, skilled personnel, and in very partial part of simple technical data. Erase everything below the waterline, and you have to recreate it before you can have your disposable electronics and internet again, a process which can very much take centuries.
