Why rating starts from 400??

I got lucky by getting high-rated opponents in bullet so my rating became good in that. Why is my blitz rating showing just 1095 lmao. How to get high-rated opponents in that also?

When creating an account you can choose a skill level and that determines your initial rating.

https://support.chess.com/article/671-how-do-i-create-an-account

The site uses the Glicko rating forumula which includes a measure of rating uncertainty called the rating deviation (RD) value. Players with few games in a rating pool with have a higher RD and their ratings will change a lot after games. As more games get played, that value drops as does the magnitude of the changes.

So, if your skill level is good enough, your rating will increase. You can also set some parameters on your challenges: https://support.chess.com/article/1962-how-do-i-choose-what-rating-my-opponents-are