They do it because they need to check for the impact of a number of things that affect the historical temperature data.
For land meteorological stations, instruments have been changed. Screens around the instruments were added. Some sites were moved introducing a material step change in results. Some stations were affected by shading from overgrowing trees. Some were affected by urban build up around them, gradually adding absorbed local heat from buildings and asphalt etc. Scientists have checked the impact of all those factors and adjusted for them.
In the USA they progressively moved from reading temperatures in the late afternoon to early morning, so that introduced a progressive cooling of results as more and more stations were giving morning rather than than afternoon readings. Scientists have corrected for that.
For ship results, historical temperature readings were taken from buckets pulled up from the side of ships. Changing that to measuring at engine cooling water intakes on board the ship reduced the time for ambient temperature to affect the water temp of readings, so later readings were relatively cooler than bucket readings. Scientists have adjusted records for that.
David Dubyne, who runs the web site that created the vid you posted is a BA grad in marketing and journalism who has also done a couple of one year courses in mandarin. His linked in page also shows he has some experience in marketing biodiesel in China and Nepal, edited OilSeedCrops magazine, did some loan facilitation into Myanmar and ASEAN markets and more recently markets and brokers cryptocurrencies. Somewhere in the middle of that he set up the web site that vid came from and he is editor and producer of that.
His vid simply borrows from a number of the non-science blog sites and packs it altogether in one vid. And those blog sites have a track record of being funded by fossil fuel funded think tanks or the like. Try reading Oreskes book 'Merchants of Doubt" on how tobacco and fossil fuel interests have used this approach to deliberately spin doubt.
I'd back NASA and NOAA against Dubyne absolutely every minute of every day.
