Why not supplemental materials?
Data control: cannot be updated, unlike materials available at data repositories.
Interoperability: If publishers only allow text and PDF formats it hampers data sharing and it will be difficult to reuse the data
Availability: Difficult to access if the article is behind the paywall (supplemental materials are not included in the DOI and therefore the links can also break!)
Not FAIR: Data/Software available in supplemental materials is not considered to be FAIR (Findable, Accessible, Interoperable, Resuable) - since they do not have a DOI assigned to them specifically (see also the Availability point above).
Impact: Data should be a primary research output
Publisher requirements: Some publishers recommend using a data repository instead
Size limits: There may be size limits in place of how large or how many supplementary materials can be shared.
Links to supplemental materials may also break, as demonstrated in the example below:
There are many reasons not to use PDFs for sharing data, the chief of which is that data shared in PDFs is dead data that can be almost impossible to extract and reuse. PDF data is frequently found as supplementary information on journal websites, but journals often migrate platforms which can break URLs; this is evidenced by the almost 60% of PDF data that was not found in this analysis.