Because it has absolutely awful throughput. Electron-beam lithography has an output measured in days per wafer. Meanwhile, EUV can easily output 150+ wafers per hour.

When the choice was made to go for EUV, E-Beam was actually the most mature technology available for next-gen lithography - but it just wasn't economically viable. The technology has remained in development over the years, but not a lot has changed yet.

If you want to know more about the topic, I can strongly recommend this video from Asianometry: https://www.youtube.com/watch?v=RmgkV83OhHA