Monero's difficulty has soared a lot in the last days and the trend seems to be confirmed.
Why did it happen? What is the technical reason?
The difficulty is a numerical representation of how long on average it will take to create a valid block that satisfies the Proof-of-Work algorithm being used, it does not represent minutes or time per se. but instead is an integer number that makes the PoW calculation take longer to perform, this is adjusted by the nodes and miners so that on average it ensures the network creates blocks at a generally consistent rate. This is calculated among all the nodes and miners in accordance with the globally agreed rules in the network, AKA consensus rules. Miners that do not include this number in their difficulty calculations will not have their block validated and included by the rest of the network.
You can find the answer here: Blockchain properties: what are Height and Difficulty?