After performing a diesel purge (bottle method) why are the filters changed?

Good measure? Risk of plugging? Will be plugged? Diesel purge somehow damages them?

There is no overwhelming reason to change any filter following the use of Diesel Purge.

In this case you have a tank & fuel system full of bugs, your filters are blocked (see your previous thread).
Until the rest of the system is clean you will continue to have problems. The diesel purge only cleans the IP & injectors.
For a normal purge, Tango is correct.

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1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving