When you upgrade software in most cases you end up with a lot of trash that requires a cleaner to remove even after the install cleanup especially when you use custom apps on the hardware you upgrade.
Most software upgrades use more ram that the previous versions do and more processor power.
It is like with win 3.1 you could load pages in about 3 seconds on a 512k line, now it takes about .03 seconds to load a page on a GB line because there are 1000 times more pixels to load and 10,000 more requirements in the access string to fulfill to display the page.