Publishing in journals or appearing on a conference largely depends on the field itself. In IACR community specifically (afaik) - conferences and workshops (small conferences) are the main source of review, discussion, and innovation, partially because the community is not that big. After each conference something like an almanach (really fat journal) is published, containing all the works presented on the conference. Most of the review is happening pre-conference where all works have to pass strict verification in order to be accepted. Apart from it, as far as I know, journal publications are not that popular in the IACR community. That’s why IOHK is making this emphasis on conferences, because the company consists of actual cryptographers, and they are excited to be accepted. In medical, for example, (afaik) as in some other fields too - journals is the prevailing way of getting your work published. Journals have editors and they ask community members for reviews, or rely on a review committee, and conferences are not that popular at all.
In IACR big conferences (where IOHK are targeting with their major papers) are not that often, but they are a source of major reputation, so they attract top people from the community who serve as a review committee and feel obliged to reject as many papers as they can, first to protect the community from all the hype and amateurism they can’t stand and because passing a bad paper would mean they get blamed for a bad review later when other serious people start to look into it after the publication
Just as a note on why conferences are important specifically in the cryptography.