What was/is impressive about MariaDB is their ability to sell to a large swath of users, from Mom&Pop shops to some of the very largest enterprises[1]. In the ServiceNow case, each customer has their own entire db and the magic is in orchestrating all of this.
Where MariaDB really shines and drives usage is around their ColumnStore[2].
Some of the downsides from a larger adoption and integration standpoint is the BSL license[3]. Relatively unknown and untested and as a result there's aversion to risk.
To get the direct answer to your question, I think a combination of the factors previously in conjunction with revenue being eroded from cloud offering their tech as a service, and SkySQL[4] not making up for the difference are serious inhibitors to revenue.
