1. Because you've already maxed out your DIMM slots 2. For the cost of upgrading to larger RAM is prohibitive because you have to throw away your existing DIMM

1. Because you've already maxed out your DIMM slots 2. For the cost of upgrading to larger RAM is prohibitive because you have to throw away your existing DIMMs and replace them with new-to-market DIMMs that are extortionate because they've only just appeared