At David already notes, it can be difficult to reach a DHCP device if the network devices don't have already have an IP. Plus depending on how you're doing routing, one router may want, or even really need, to know what the other side's IP will be. With most DHCP hosts, they are not the target of other hosts, beyond replying to them.
In the real-world, for years, Cisco network devices didn't support DHCP on their own interfaces, and now that some do, it's often only used for dynamic connections to an ISP, where the whole site, behind it, only expects external hosts to respond to its hosts, not be the target of initial requests.
For "ordinary" hosts, in a lab, again as David notes, as there's often so few, using DHCP it's generally much more work to make it work, than just placing an IP on a few hosts.
Laugh, in the real-world of networks, I was the crazy guy who wanted most servers to use DHCP, as they too, unlike client hosts, even though they too, are "targets" of other hosts.
(Generally, not an ideal liked by server folk, but for most servers, they cannot show a reason not to do it. However, great grandpapa, grandpapa and papa, all hard coded IPs on server hosts, and, by Jimmy Cricket, if it was good enough for them . . . [Laugh, to be fair, there are network engineers who believe you must hard code speed and duplex on infrastructure copper links for about the same reason. {Personally, I don't automatically think great grandpapa, et al, were stupid. They may have very well had a fantastic reason for what they did. But, what's the reason, and does it still apply? Possible true story - which goes - current person cooking a turkey in oven - cuts it in half, and cooks each half separately. Significant other asks, why? Person responds, that's how I learned it should be done from my forebear person. Later, forebear person, who's still living, is at person's house, and sees person cutting turkey in half. They also ask, why? Person responds, but that's how you always did it. Foreperson says, well yes I did, but that's because my oven was too small to contain a full sized turkey.}])
