Because people do it wrong. Sasae is more of a block. Hiza means "knee "wheel". Your grip is more circulair in motion. You block the knee in Hiza but the hand motions are different.
If you block the knee it is hiza and anything below the knee is saesae. The arm(s) motion is different. Saesae I see it performed on the collar side of the opponent and hiza on the sleeve side of the opponent. Also saesae is usually performed stepping into the opponent where Hiza is usually performed getting the opponent moving toward you or in a circle.
Best Saesae I have seen in competition: https://youtu.be/H8imPoRAz9Y
You said it better than I could. LOL
Sobirov is a master of sasae. Some good examples in this highlight including the one at the 1:10 mark. As judoblackbelt mentioned you generally step in close to execute a sasea, but with hiza you need more space so you can block the knee.
Member Since: 3/28/07
That is definitely Sasae at the 1:10 mark and 2:13 mark. He was the complete judo player. Various throws, sacrifice throws, counters and ground techniques. Amazing quickness, beats the opponent to the punch so to speak.
I do not see him ranked in -60k or -66k so he must of retired at age 32.