Since d3839617 in details view mode clicking anywhere within the row is considered a click on the item. That commit also changed it so that dropping files anywhere inside a row would make it so the files are received by the folder of that row.
This commit reverts the drop behaviour to be identical to the old one.
I am having trouble explaining why this is better because one can look at it in different ways. Bottom line is that one doesn't really feel like one is dropping files inside a folder unless the mouse cursor is actually directly above a folder's icon or name.
Another argument is that it is normal behaviour to just throw files onto an application and the files then being opened by it. Having potentially large parts of the view area covered by the rows of folders means that there has to be more of a conscious effort to not drop the files inside one of the folders by accident while with this commit one has to aim precisely onto a folder to do it intentionally.
Related bug report with multiple mentions of this being an issue: https://bugs.kde.org/show_bug.cgi?id=453700