ThrashZone This is all because you do wrong assumptions and you suppose everyone thinks like you....
Software center isn't different from a store. Imagine you go in a computer store, you can buy a motherboard designed for Intel CPU and also buy an AMD CPU... Still you won't be able to magically plug the AMD CPU on the Intel motherboard because you got them from the same store !
As the name clearly states mate-sensor-applet : Sensor applet for the MATE Panel which is available in the category Desktop Software & Teaming -> MATE Desktop is a component of the MATE desktop.
Same way plasma-vault (for example) : Plasma applet and services for creating encrypted vaults which can be found in the category Desktop Software & Teaming -> KDE Desktop is a component of the Plasma Desktop.
By the way you will have exactly the same problem with linux mint. If you install the Cinnamon edition and try to install MATE applets (or the other way around), it won't work.... And again the problem would not be their Software center...