Probably because it is a "dumb iron" with no thermal control. As soon as it touches anything it cools way down. Nowadays fortunately, cartridge tip irons are cheap if you're willing to buy from China. Cartridge tips have the heating element and temp probe built directly into the tip, heat up and adjust extremely fast to thermal loads.
As mentioned, you need the pad to be hot for the solder to wick onto it. There is missing info in step 1.
Step 1 should say to have a slightly wet iron (solder on the iron). You used this molten solder as the heat transfer medium. Hold the iron so the wet solder on it is touching the pad and lead. This gives more surface area for the heat to travel from the iron to the pad.
A dry iron touching a pad will have poor thermal connection, so the pad will take a long time to heat up.
I think an apt comparison is touching hot stuff with a wet glove. With a dry glove, the heat has to conduct through the fabric before heating your hand. With a wet glove, the heat is conducting through the water and burning your hand. The solder, like the water in the wet glove, is a bridge for the iron to transfer heat efficiently to the pad.
I think a lot of hobby soldering guides really neglect the idea of heat transfer and thermal mass.