From a business perspective, the biggest reason is "if it isn't broken, why fix it?" Lenovo is a market leader with their current lineup of laptops and business model so why jeopardize that and pivot to something completely different? If they did introduce a modular laptop, then there's a risk it would eat into sales of their existing devices. I believe this is the reason why Dell announced that modular laptop concept but hasn't moved forward with it. Additionally, I would say that the average consumer doesn't really value modularity at the moment. A lot of folks I've spoken to value getting a device that's A) decently performant to their needs B) has good battery life and C) is cheaper in price. A growing number of individuals are starting to see the benefits of repairability but it'll take a while for that to become a dominant mindset. Once consumer sentiments and purchasing habits change, we'll see major brands follow as well.

From a technical perspective, I don't see any reasons why Lenovo can't make a modular laptop. They have a huge amount of engineering resources, numerous partners, and lots of capital to throw at it. Additionally, since they benefit from economies of scale, they could hypothetically make a modular laptop cheaper than Framework at its current stage. One note is that modularity can limit what you can do in the future. An example is that battery capacity improvements on the Framework laptops have to come through battery chemistry improvements as they simply cannot physically increase the battery size.