Walmart has been making lots of e-commerce acquisitions, Jet was just the biggest. A lot of it is about growing outside of the traditional walmart customer- High end brands won't sell on walmart.com, and even if they did, high end shoppers don't go to walmart.com, but they have no problem going to Jet, or Moosejaw, etc. Jet was also framed as an acqui-hire of their management team, in particular Marc Lore. How true that is, I can't really say- another way to put it is, this seemed to be a move that came from above e-commerce.
The strategy is more about reaching different customers, and gobbling up potential competitors while they are small. The frontends may look a lot different, but its all one backend (or at least that is the end state for these acquired companies).
From my perspective, Walmart.com is finally seeing customer facing improvements as they have finally completed the backend re-write and migration which took literal years and held up most customer-facing work. Rewriting the FE, while not a small undertaking, is actually not that difficult to do with their architecture. Compare that to say Amazon, who I interviewed with, and they admitted that changing say the "Amazon orange"color to something else would be a herculean effort involving a year of planning across the entire company and lock step releases across the company. They seemed to think they had a better way of doing things, but after hearing that, I wasn't so sure I wanted to work there.