Pure Land is very large and very badly counted. No credible standalone figure exists for it worldwide, and the Japanese numbers in circulation are institutional self-reports rather than survey results. Jodo Shinshu describes itself as the most widely practised form of Buddhism in Japan and claims a following on the order of a tenth of the population; that is an organisation's claim about its own affiliated households, and Japanese temple affiliation is largely inherited and largely funerary.
The wider picture is that recitation of Amitabha's name is ordinary practice for a very large share of Buddhists in China, Taiwan, Vietnam, Korea, Japan, Singapore and Malaysia, and among the East Asian diaspora everywhere, including a great many who would not describe themselves as belonging to a Pure Land school at all. It travels particularly well among people with no monastery within reach.
In the West, Jodo Shinshu has one of the longest institutional histories of any Buddhist body. The organisation now called the Buddhist Churches of America was established among Japanese immigrants at the end of the nineteenth century, and its members were interned with the rest of the Japanese American population during the Second World War. It remains an ethnic-community church far more than a convert one, and receives correspondingly little attention in Western writing about Buddhism, which has concentrated on the meditative traditions.
That neglect illustrates the general point rather well. The devotional forms are the majority of Buddhism and a small minority of the coverage.