There is one additional filter to the mimetypes being extracted here, at /usr/share/tracker3-miners/extract-rules/15-text.rule:
[ExtractorRule]
ModulePath=libextract-text.so
MimeTypes=text/plain;text/markdown
FallbackRdfTypes=nfo:Document;nfo:PlainTextDocument;
Graph=tracker:Documents
Hash=d35fd368fe97892c95134d493a67d39834817454eec787cddc36b8e1ca5612c3
As seen in your output, the .log files get a distinct text/x-log mimetype not covered by this file, I suppose the other files also have distinct mimetypes that throw the plain text extractor off.
With the configuration setting in place, it could make sense to consider generalizing the extractor to let additional mimetypes through. Please file a tracker-miners issue for that.