why it is not installed on laravel 6

[aswathipavi]

composer require spatie/laravel-medialibrary
Using version ^7.19 for spatie/laravel-medialibrary
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Conclusion: don't install spatie/laravel-medialibrary 7.19.3
- Conclusion: don't install spatie/laravel-medialibrary 7.19.2
- Conclusion: don't install spatie/laravel-medialibrary 7.19.1
- Conclusion: don't install spatie/laravel-medialibrary 7.19.0
- Conclusion: remove maennchen/zipstream-php 2.1.0
- Installation request for spatie/laravel-medialibrary ^7.19 -> satisfiable by spatie/laravel-medialibrary[7.19.0, 7.19.1, 7.19.2, 7.19.3, v7.x-dev].
- Conclusion: don't install maennchen/zipstream-php 2.1.0
- spatie/laravel-medialibrary v7.x-dev requires maennchen/zipstream-php ^1.0 -> satisfiable by maennchen/zipstream-php[1.0.0, 1.1.0, 1.2.0, v1.0.0-alpha.1, v1.0.0-alpha.2].
- Can only install one of: maennchen/zipstream-php[1.0.0, 2.1.0].
- Can only install one of: maennchen/zipstream-php[1.1.0, 2.1.0].
- Can only install one of: maennchen/zipstream-php[1.2.0, 2.1.0].
- Can only install one of: maennchen/zipstream-php[v1.0.0-alpha.1, 2.1.0].
- Can only install one of: maennchen/zipstream-php[v1.0.0-alpha.2, 2.1.0].
- Installation request for maennchen/zipstream-php (locked at 2.1.0) -> satisfiable by maennchen/zipstream-php[2.1.0].

Installation failed, reverting ./composer.json to its original content.