IMO LEGO thrives thanks to their relentless focus on product quality. The phrase "det bedste ir ikke for godt" (roughly "only the best is good enough") has a long history in the company. The fact that they have been able to thrive like this in a market with many competitors cloning their product is a a testament to their product quality and related brand strength.
If you've used and compared the various brands in this space, you'll be familiar with the quality variations. LEGO has put immense engineering effort into having the best plastic and tightest tolerances in the industry, and I can really feel the difference when building.
Here's one example comparing some of the clone brands to LEGO's own products:
Other brands do continue to improve, and there are many companies out there that make very nice building toys, but LEGO has done a nice job making sure that everything they ship is of good quality.
If you've used and compared the various brands in this space, you'll be familiar with the quality variations. LEGO has put immense engineering effort into having the best plastic and tightest tolerances in the industry, and I can really feel the difference when building.
Here's one example comparing some of the clone brands to LEGO's own products:
https://uploads.brickset.com/docs/clonebrands_v1.7.pdf
Other brands do continue to improve, and there are many companies out there that make very nice building toys, but LEGO has done a nice job making sure that everything they ship is of good quality.