Yet most of the old technologies we've invented are still used by hobbyists and collectors. Morse hasn't ceased to exist, neither have steam trains, analogue radio or horses. None have been forgotten. People are still making crystal sets and wave traps. There's a whole niche on YT of people making primitive huts, fires, bows or making it their weekend hobby through re-enactment etc.

Some of the details are lost like maintenance details, advanced fault finding etc, but the core remains.

After a century of radio and electricity it would be rather silly to only search for other signs of life on the new system of FTL communication we just discovered. It still gives no certainty that the candidate alien discovered the same defacto standard for FTL comms or that theirs will be recognisable.

Any rational search should try and encompass both and probably still emphasise the analogue as any advanced civilisation would very likely go through that phase first, just like we are. We'd be likely to catch more possibilities that way.