Weird thing --onclick event disappears when I switch the visual and text tab

[admin]

here is the piece of code I want to add the wordpress page:
<img src="

https://imgur.com/8B6dp

" alt="enter image description here">
But when I click visual tab and come back to text tab. The onclick event disappeared:
<img src="

https://imgur.com/yj3pu

" alt="enter image description here">
<img src="

https://imgur.com/a4VeU

" alt="enter image description here">

<strong>Can anyone explain why it happens? why do it change the code when I switch the visual and text tab! Thanks in advance!</strong>