I once read (ages ago, can't find the source now) that it is deliberate - because with mass produced consumer goods such as shower gel or body lotion etc. if you throw away the last 2-3 uses because they are too hard to get out of the bottle, you will buy earlier and hence more of their product. They give you effectively less than you pay for, and it adds up for them. And they get away with it because it's your choice to rather buy a new bottle for convenience. So of course, it's again because corporations are only interested in cutting corners to give you the minimum viable product possible.