Why are all NFC tags NTAG213 ?
Almost all NFC tags for sale are NTAG213. Why ?
There's two reasons.
First is that it is a good all round chip which has enough memory for the vast majority of applications and a number of extra features, such as a counter, that make it easy to use. Buying and manufacturing NFC tags and chips is a volume business. They more that are made and purchased, the cheaper the price. So it becomes easier to gravitate towards a single chip to keep quantities high - and priced down.
Second is a legacy marketing factor. Before the NTAG213, there was the NTAG203 - the first of the NTAG series chips. At that time, there was only the NTAG203. When NXP, who make the chips, launched the 21x series, they also launched a number of other similar chips such as the 215 and 212. However, the market, and sellers like Seritag, had already grown uses to the 203 and the 213 was the effective replacement. So the 213 became the new normal chip.