The problem is that having user-serviceable parts significantly adds to the bulk of a device, and it's pretty clear that's not an appealing tradeoff to most users and manufacturers.
E.g.: just to have a removable battery, you have to put a protective case on the battery as well as an internal "case" to receive the battery inside the device (generally, another layer of plastic. Even on laptops that is becoming prohibitively bulks; on tablets, it's a non-starter (see the recent MacBook Pro redesign). You just can't pack the parts together tight enough and still have them be user-replaceable.
I love the idea of a modular mobile device as well, but it's pretty clear things are headed in the other direction: thinner, sleeker, longer-battery-life products sell better than bulky but more customizable products.
E.g.: just to have a removable battery, you have to put a protective case on the battery as well as an internal "case" to receive the battery inside the device (generally, another layer of plastic. Even on laptops that is becoming prohibitively bulks; on tablets, it's a non-starter (see the recent MacBook Pro redesign). You just can't pack the parts together tight enough and still have them be user-replaceable.
I love the idea of a modular mobile device as well, but it's pretty clear things are headed in the other direction: thinner, sleeker, longer-battery-life products sell better than bulky but more customizable products.