Depending on whether you are using biblatex or BibTeX, the .bbl file might not really lend itself to being read back by a machine if you want to recover all data. If you only want to recover which entries were cited and no additional data, that is less relevant.
The .bbl file produced for BibTeX bibliographies contains typesettable text and thus requires quite intricate parsing if you want to get back the entry data.
\begin{thebibliography}{1}
\bibitem[Elk(1972)]{elk}
Anne Elk.
\newblock \emph{A Theory on Brontosauruses}.
\newblock Monthy \& Co., 1972.
\end{thebibliography}
Since the style decides what gets written to the .bbl file, some data might be missing.
The .bbl file produced for biblatex contains entry data in a structured, LaTeX-readable format that could in theory be parsed to get back all entry data.
\refsection{0}
\datalist[entry]{nyt/global//global/global}
\entry{elk}{book}{}
\name{author}{1}{}{%
{{un=0,uniquepart=base,hash=6a9b0705c275273262103333472cc656}{%
family={Elk},
familyi={E\bibinitperiod},
given={Anne},
giveni={A\bibinitperiod},
givenun=0}}%
}
\list{location}{1}{%
{London}%
}
\list{publisher}{1}{%
{Monthy \& Co.}%
}
\strng{namehash}{6a9b0705c275273262103333472cc656}
\strng{fullhash}{6a9b0705c275273262103333472cc656}
\strng{bibnamehash}{6a9b0705c275273262103333472cc656}
\strng{authorbibnamehash}{6a9b0705c275273262103333472cc656}
\strng{authornamehash}{6a9b0705c275273262103333472cc656}
\strng{authorfullhash}{6a9b0705c275273262103333472cc656}
\field{sortinit}{E}
\field{sortinithash}{8da8a182d344d5b9047633dfc0cc9131}
\field{extradatescope}{labelyear}
\field{labeldatesource}{year}
\field{labelnamesource}{author}
\field{labeltitlesource}{title}
\field{title}{A Theory on Brontosauruses}
\field{year}{1972}
\endentry
\enddatalist
\endrefsection
\endinput
The .bbl file generated for biblatex will contain context-specific data that is only relevant within the current document context. This may or may not be wanted when you want to export the data to .csv.
But I would go down a different route. I would use one of the methods from Creating .bib file containing only the cited references of a bigger .bib file to generate a .bib file of only the cited references and would then use a library to read in the .bib file directly.