What kind of link building strategy is this?

I see a lot of my competition sites using this kind of forum linking spam to rank for various keywords. Although these aren't my competitor links, they might help you guys in guessing the idea behind this. They are ranking with a lot of such links and some high DA Guest posts.

http://aandp.net/forum/showthread.php?tid=192017
http://mundo.osyley.com/viewtopic.php?f=4&t=505412
http://www.infoaudifonos.net/foro/8-foro-para-usuarios-de-audifonos/362433-just-dance-2019
http://coryn.club/forum/viewtopic.php?f=28&t=408180

The competitors are still going strong and ranking even after multiple algorithm updates. what are they doing? Is there any tool for building forum backlinks like this?
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