Why was leg grips banned in judo?

What is the name of this takedown / throw?

Wrestling firefighters wear

It sounds like you're talking about a variation on the wrestling firefighter's carry. I'm not sure if actually picking up the opponent in wrestling changes the classification. The instructor in this video definitely cancels himself completely in one example, but appears to go straight to the victim in another.

Judo uki waza or yoko otoshi (formal), kata guruma (informal)

In judo this was called Kata Guruma. However, if you are using a sacrificial technique, it is not the current formal classification. For understanding the arcane formal judo classification is Kodokan Judo: Throwing Techniques by Toshiro Daigo, Kodansha, Tokyo, Japan 2005 the best source. Toshiro Daigo, the current head of the Kodokan, said a victim in the Kata Guruma position would be either Uki Waza or Yoko Otoshi.

Daigo p. 232 discusses "Uki-Waza from the form of Kata Guruma":

According to a study by the Kodokan Waza Research Institute (April 1, 1997) it was decided that this technique is related to Uki-Waza and not to Kata-Guruma, since the concept of throwing is based on the principle of Yoko-Sutemi. Waza [side sacrificial technique].

Daigo p. 235:

It is extremely difficult to clarify the differences between these techniques [yoko otoshi and uki waza] and it is a matter for the judges.

The judo throw classification points can be quite complicated and opaque. I would recommend not investing too deeply in understanding current Kodokan thinking about the differences between Uki Waza and Yoko Otoshi. In daily use, I would also expect this to be called Kata Guruma, as it is in the linked YouTube video, as the official word for it only dates back to 1997.

user8472

It's not Firemans Carry or Uki Waza. My leg grip was from the ankle and the throw itself had nothing to do with my shoulders. Yoko otoshi comes a little closer, but instead of tripping the leg with my leg, I used my hand to lift the leg off the floor.

user8472

What Comes to Kodokan and Judo Techniques in General; Judo died for me when they banned all leg grips, so little details of a throw classification don't really interest me. I just want to get better as a grappler in general.

mattm ♦

Yoko Otoshi doesn't have to block the leg. The most important point is to unbalance the opponent and to throw them to the side when falling. Blocking the leg is optional. I often find that falling too close to your opponent is ineffective while falling further away is more difficult.