Could it be that it is due to the quite slow hardware, even though I know that it is able to push more traffic?
I notice too your relay got the guard flag very recently. So your relay is currently probably not at full capacity and rather at a low one (relay usage drops at guard flag assignment). You have to wait 60 days from your guard flag to reach this point.
See https://blog.torproject.org/blog/lifecycle-of-a-new-relay, you’re currently at the beginning of the 3rd phase.
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