the number of definitions do they really have to decrease or increase?

am now at 5.881.669

Yeah.Back in 2010 avast blog post will help you.
https://blog.avast.com/2010/09/06/spring-cleaning-in-our-virus-database/

You shouldn’t be concerned about the amount of definition since a single definition can detect x amount of malware.

Signatures by their very nature will fluctuate, there are thousands of new malware signatures every day.

Over time the virus/malware signature database would become massive to a point it could slow scans. The database is constantly optimised so signatures detect more than a single virus/malware variant. This has the effect of reducing the number of signatures in the database.

Thank you …just that iv been observing it for a while now but i noticed that they were reducing but anyway thank you i understand now

You’re welcome.