The common answer here that “Japanese names are easier to pronounce” is technically correct, but it’s not the main reason why Japanese don’t use English names.
The actual reason has to do with immigration to the US. Both Chinese and Japanese immigrants to the US took up English first names. The split happened because of the outsized influence of Chinese Americans in China. Damn near half of all prominent Chinese in the first half of the 20th century had experience living abroad. By contrast, Japanese Americans rarely had any impact back in Japan.
David Suzuki is one of the very few prominent Japanese Americans/Canadian. Unlike the vast majority of Japanese people you can name, his family has been in the US/Canada for multiple generations.
George Takei is another good example. Despite his fame in the US, barely anyone in Japan knows him (Star Trek doesn’t have much of a following in Japan).
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These Chinese Americans were the first ones to introduce the concept of adopting English first names to Chinese back home. Prior to this, Chinese in China always used their Chinese names when dealing with English speakers.
With the opening up of China in the 1980s, millions of Chinese emigrated to the US, and many of them returned to China, kickstarting the modern trend of Chinese in China giving themselves English nicknames for dealing with foreigners. This immigration back and forth didn’t happen in Japan with any comparable level of numbers or influence.