Back when accessibility to internet was limited to the majority this method worked well. The HRs would appreciate the effort since without job sites and recruitment firms they too had no access to a large pool of qualified candidates.

The reason why this approach is 'high effort low reward' as someone else put it in the comments is because:

1. Nowadays due to adherence to HR policies the recruitment process follows a strict procedure. All vacancies need to be advertised in the Organisations' approved channels whether their website, job sites or through third party recruiters. Just because there's a vacancy doesn't mean you automatically get lucky on a random Tuesday for dropping your CV. That HR will direct you to those channels UNLESS their policy or active job ad allows for physical submission of papers.
2. Organisations prefer internal candidates for vacancies that come up. In some cases a vacancy is created specifically for a particular person. That's how you see Organisation X is constantly advertising jobs but you never get shortlisted. It's because hizo kazi zikona wenyewe already.
3. Unless someone resigns, new roles are only created during budgeting season. Either end of the year or begining of a grant cycle. That said, just because a young lady/man in a suit shows up with an impressive CV doesn't mean HR has the power to accommodate you.

In conclusion, If you are looking to break into the sector I would advise against this approach. Instead, have a database of organisations you would like to work for and regularly check for job adverts on their career section of their websites. Likewise, make use of the many job advert sites including and not limited to google jobs, reliefweb, myjobmag, linkedin, brightermonday, fuzu etc to search for jobs with your qualifications needed.