Hi Anu,
this is a knoiw challenge and there could be different reasosn for that, not necessarily a technical issue. The more MP you import in your SCOM management group, the more configuration the agent has to process, the larger the .db file. There is also a MP that deals with certain aspects of that:
Management Pack to Monitor and Reduce Health Service Store Size
https://techcommunity.microsoft.com/t5/core-infrastructure-and-security/management-pack-to-monitor-and-reduce-health-service-store-size/ba-p/365803
In a blog post by Martin Ehrnst you can find also some nice anlysis and suggestions (for example defragment the .edb):
HealthServiceStore.edb file growth
https://adatum.no/operationsmanager/healthservicestore-edb-file-size
Those two sources will give you an idea on how to solve this.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Stoyan Chalakov