If that's true it's only because most people don't understand these pure maths fields. But their results are generally very useful to the applied mathematicians (whose results are and should be used in most other fields) and in this way there is still an impact although it's not always reflected in the citations.

The fact is that these pure mathematicians could almost surely write the more applied papers but don't because it would feel to repetitive. You don't need to read Euler's work in order to indirectly benefit from it. It's the same for a lot of pure math.