Custom Gutenberg block is not showing up in inserter dialog

You should enqueue your scripts using enqueue_block_assets action, like this:

add_action('enqueue_block_assets', 'gutenberg_bolierplate_block');

Second, you should use JSX with modern JavaScript development environment to write your blocks easily.

I made a boilerplate for my personal use that you can use: https://github.com/HardeepAsrani/gutenberg-boilerplate

You just need to run npm install to install dependencies, and then npm run dev or npm run build to transpile the code.

If you want to continue this way then you will have to edit the first line of your code from

var el = wp.elements.createElement,

to

var el = wp.element.createElement,

As it uses wrong module name.