Dear colleague: I asked myself the same question a long time ago but came to terms with it. Let me enumerate some of the contributing factors to this practice:

1. They may have more time to spare for research than others.

2. They (almost) certainly have the necessary knowledge to be prolific authors.

3. They may co-author research with their own Ph.D. students (a practice very popular in Western countries).

4. Their own students may author things for them and they just append their name to the manuscript.

5. They may have the potential to recycle their knowledge of the same topic by publishing it in various outlets across the world.

6. And last, but not least, they may want to publish in fee-paying journals that publish you anything, unfortunately.

In physical sciences with large experiments or difficult observations and large and expensive equipment like nuclear physics, astrophysics and space science, publications with a large number of authors are quiet common. With many co-authors it is possible to published dozens of papers per year. See also these discussions:

https://www.researchgate.net/post/What_do_you_think_about_multiple_author_papers/1

https://www.researchgate.net/post/What-do-you-think-about-articles-where-the-list-of-coauthors-is-bigger-than-the-article-itself/1

https://www.researchgate.net/post/Group_Authorship_is_there_a_minmum_and_maximum/1

https://www.researchgate.net/post/Is_there_a_limit_to_the_number_of_authors_on_any_scientific_publication_regardless_of_disciplineWhat_is_the_number_of_restrictions_if_there_are_any/1

https://www.researchgate.net/post/How-many-maximum-number-of-authors-are-enough-in-a-research-paper/1

https://www.researchgate.net/post/Mesmerizing_list_of_authors_5_154_in_one_article_research_break_through_is_a_group_activity_but_do_we_need_to_include_whole_community/1

https://www.researchgate.net/post/What_do_you_think_about_single_author_paper/1

https://www.researchgate.net/post/Single_author_papers_vs_multiple_ones_which_ones_have_more_value/1

https://www.researchgate.net/post/Solo_author_vs_multi_authors_papers_which_is_more_reliable/1