I know it's not a satisfying answer but this is standard practice for professional power tools. Most tradesmen have a pool of batteries that they take from for whatever equipment they happen to need, be it a vacuum cleaner, circular saw, sander, angle grinder or whatever else.

It'd be a waste for them to pay for new batteries for every new tool they buy when they already have a pool of batteries.

Plus, batteries for these tools come in a wide variety of sizes and the bundled battery would likely be the smallest. Better to give the customer the choice of which battery to buy in case they want a bigger one.

As for offering, Galaxus does offer the batteries and chargers. Here's the pack I bought when I bought this vacuum: Bosch Professional Battery charger GAL 1880 CV Set incl. 2x 5Ah battery (18V, 5Ah)

Yes, that pack is expensive. Again, this is the professional line of tools.

If you don't want the professional line of tools, look for the green Bosch vacuum cleaners. If it's green, it's the consumer line. These will come with bundled batteries and chargers. Here's one example: Bosch UniversalVac