can i get vo2 max measurement when cycling

If you can’t find any VO2 max readings in the Health app, that is probably because you have not yet logged the right kind of workouts with your watch. Only two workout types can produce an estimated VO2 max on Apple Watch: Outdoor Walk and Outdoor Run. (However, I believe Hiking also works.)

VO2 max relates to maximal exertion. So you’ll need to log a pretty intensive workout to generate a reading. And you’ll need to sustain it for at least 20 minutes.

This is a user-to-user forum. No one here (with VERY limited exceptions) works for Apple. So we really can't (and don't know) the answer why questions. If you would like to make this suggestion to Apple, use this link:

Product Feedback - Apple

Perhaps if you really want a definitive answer you could use the 'Get Support' link at the top-right corner of this page, but I doubt you will get a satisfactory answer.

You'll only get a measurement by outdoor running,walking or hiking.