Well it’s not usually a hippo – it tends to be one of any number of large objects – but let’s use that as a metaphor and substitute anything else as appropriate. It is often used as an absurd attempt to claim that nobody can ever cycle or walk for transport, ever, and is usually accompanied by a self-satisfied, triumphant expression. Never mind that you probably can’t carry a hippopotamus in a Range Rover, either; that seems to be quietly ignored.
Of course, this is an example of a straw man; nobody is suggesting a ban on all motor vehicles. Of course motor vehicles are needed for some purposes. So what? We can still use them when needed. However, there are huge numbers of journeys for which they are not necessary.
In fact, there are cargo cycles available that allow you to carry all sorts of things; some of them electrically assisted. In fact, there are companies delivering all manner of bulky items by cycle nowadays, when the infrastructure is in place to allow it, and they are often cheaper, faster and more efficient than using vans. On those occasions when that really is not possible, you could use … er … a van!