According to the Above Screenshot, You have allocated all Named User licenses that were available to the Users (4 Users). As we can see from the below Image, we have only 4 Named User Licenses in the Community Version.
If you need more, you could try Requesting for a Enterprise Trial and then Check if you can allocate more licenses again.
As noted above by @supermanPunch, Community allows for 2 Attended & 2 Automation Developers in addition what is not shown in the screenshot also 1 Unattended.
As Studio/Developer is also considered an Attended Robot this would account for 2 of your users in addition to the 2 Attended licenses allowing you provision 4 users that can run a process in an attended state.
Community edition is not intended for a scale of 50 users, and as you can see the Enterprise Trial is not sufficient either as well as being a time based trial. In order to satisfy your requirements you would need to purchase sufficient licenses to allow for the number of Named / Concurrent licenses that you need.
More information about the available licensing SKUs that can be purchased, can be found here
You can start an Enterprise trial and/or buy required licenses directly from your Cloud Portal under the Admin > Licenses.