Why does the right side radical of 踵 have different stroke order than 重?

Question

Why does the right side radical strokes order 踵　are different than 重 alone?

Answer 1

There are sometimes more than one acceptable stroke order. The Japanese wikipedia article on stroke order mentions that there is not always a single correct stroke order - some kanji have two or more which are commonly used, and also sometimes the stroke order changes when writing 行書{ぎょうしょ}. In 1958, the Ministry of Education in Japan published a document which showed stroke orders for the then 881 kanji on the 'education' list:

本書に取りあげた筆順は、学習指導上の観点から、一つの文字については一つの形に統一されているが、このことは本書に掲げられた以外の筆順で、従来行われてきたものを誤りとするものではない。

That is, one stroke order per character was given for teaching, but that did not mean that stroke orders which had been used in the past should be considered incorrect.

For 踵 specifically, I don't think there is an 'official' determination in Japan on how it should be written, although I agree it would be normal to follow the stroke order for 重.

It may be that some of the stroke orders on that site are taken from Chinese sources, where there are official guidelines for more characters. For example, here is an official Taiwanese source (Ministry of Education) which uses the same one as you link.