As I understand it, a similar pattern as in the present Great Britain - Neolithic y chromosomes just find of ended all at once. What were the advantages of Yamnaya (predecessor to corded ware culture) other than just equine animal husbandry? Is this Iberian shift associated with R1a or Robert? Many interesting questions.
R1a or R1b that is.
The suggestion in the paper is, pandemic and climate change (of course). "...the paternally inherited Y chromosome lineages show a complete turnover, linked to the movement of steppe-related ancestry that is also visible in other parts of Europe." Displacement, or maybe an earlier localized LGBTQ campaign of Y extinction led to invasion and domination by men from elsewhere.
Being from the steppes, the Yamnaya made great use of wheeled transports. It helped them conquer far and wide.