There is a substantial lack of large-scale infrastructure, access to materials, trade and transmission of knowledge.
In our world we have it all. You can order a USB drive from across the world, which itself is created by many precious materials from across the world, which can be combined by the knowledge we can build and maintain from across the world.
But your world does not have that. For example imagine two cities that want to trade. A dirt road is relatively easy since you just travel the distance over and over again. But now imagine building a stone road like the romans did. Monsters will attack the workers, monsters will attack the supply train that brings the food and materials for the workers, monsters might attack or eat the road itself. This makes it hard to build any lasting infrastructure without a ludicrously extensive military complex that clears the area of monsters for kilometers around.
Then imagine metalworking. Someone else answered that metal boats are superior to wooden boats because of maintenance and build methods, but that assumes you have the infrastructure and industrial capacity to mine, refine and create the metals required for the boat. If the metal mine you need is in the next country/citystate you may get a metal shipment once a month, and the amount will be low since they have to travel across hard to maintain roads and it will be ludicrously expensive compared to sending an armed guard with a group of loggers to gather wood. And that is ignoring the fact that you need metals to build the facilities that refine and shape the metals to build the facilities that build the boats. All of which you need space for and the infrastructure to transport it. Oh and monsters underground ofcourse, they might make mining even more dangerous too.
Then there is knowledge. We can study at colleges, which shares knowledge with other colleges if only to maintain a quality control. However in this case someone learning metalworking might make a dangerous journey towards a city that has the skills to teach him/her, but there is likely little reason to go somewhere else as any place that can teach metalworking has the infrastructure and capacity to get those metals in the first place.
Some places never get the metals to ever even start research in things like electricity, industrialization, basic blacksmithing... and other areas have the safety and resources to get into it. This creates disparity in technology.