There’s no reason why they can’t. 15 years ago I had a business where I refurbished ex-corporate/govt laptops and sold them online. Thinkpads for example were all modular, for example the charge socket was on a separate mini daughterboard, and IBM then Lenovo put all the service manuals online which gave instructions for fully disassembling and re-assembling them. For the T and X series I specialised in you could buy all the spares from the manufacturer. Dell didn’t give you access to the service manuals but the Latitudes and Precisions of the era were again modular and you could work out how to take it to bits fairly easily. Unlike IBM/Lenovo though they didn’t make parts available but at least you could buy spares online from say Ebay.
When they started to change to bringing out ever thinner laptops is when it all started to turn to shit but I found that Lenovo still kept service manuals online even for their retail laptops, HP too did some, albeit a bit more limited.