There's a few things going on with the corporate ones. Companies started building them in 1927, starting with the Asahi Shimbum (newspaper) who put up a monument dedicated to their deceased employees. Often they commemorate employees who have passed like the Nissan cenograph . Some of them have individual photos of the employees, usually from around the 40's onwards. Previously in Japan the whole idea of the place you work being "family" (and you working the same job your entire life) was a big thing to foster loyalty. Much like the "we're a family here" bullshit line you hear in the West, but the company might at least name you on a piece of granite when they overwork you to death.

Some of them just commemorate the founding of the company, and tend towards a status symbol humble-brag and show off how pious they are at the same time. Sort of like how In-n-out puts bible verse numbers on their cups and Chik-fil-a doesn't open on Sundays. I'd say the Denka one is along those lines. It was built for the company's 100th anniversary.

Some of them are used as gathering points for annual memorial ceremonies too like the Yakult one complete with iconic bottle design, I know there's a tradition in at least some parts of Japan to return yearly on the anniversary of a funeral to visit the family, many of these stones serve as gathering points for the companies to do memorials. Some graves are for individual business-people who were important to the company like presidents. The Panasonic grave was put in the day after they changed the name to Panasonic, the block on the left of it in the image is their original company name gravestone. They were super keen on keeping it updated.

There's also ones from probably more genuinely pious (or at least guilty-feeling) companies and organisations. Here's one dedicated to animals killed during scientific research from 1967 which I thought was pretty touching. If you google search for images for "動物供養塔" which means "animal memorial tower" you can find a bunch of different graves all over Japan with the same purpose. And here's a memorial erected by the trade association of fugu chefs, for the benefit of the souls of all the fish they have killed. which was a cute surprise. And another here from The Japanese Termite Control Association erected 1971 dedicated to all the termites it had to kill in the course of its work. Because obviously Buddhism isn't really big on the causing death thing.

A couple of extra links for anyone interested. All of them are Japanese, but google translate handles most of it really well:

• Article on corporate graves (Japanese)
• Another article on the topic, different info (Japanese)
• List of some of the notable graves with pics and some good added info (Japanese)