Bootstrap with --constraints

I’d like to have a local cloud that uses lxd VMs by default.

I’ve used juju bootstrap --constraints "mem=2G virt-type=virtual-machine" localhost lxd to boostrap with the lxd provider. From the docs my expectation was that for all future models on this cloud VM machines would be used:

...
If '--constraints' is used, its values will be set as the default
constraints for all future workload machines in the model, exactly as if
the constraints were set with `juju set-model-constraints`.
...

I could see the controller machine indeed was deployed as a VM. However after adding a model and deploying an application a container machine was added for the app.

peter@pirx ~ » lxc ls                                                                                                                                  1 ↵
+---------------+---------+-----------------------+------+-----------------+-----------+----------+
|     NAME      |  STATE  |         IPV4          | IPV6 |      TYPE       | SNAPSHOTS | LOCATION |
+---------------+---------+-----------------------+------+-----------------+-----------+----------+
| juju-1687f6-0 | RUNNING | 240.22.0.194 (enp5s0) |      | VIRTUAL-MACHINE | 0         | pirx     |
+---------------+---------+-----------------------+------+-----------------+-----------+----------+
| juju-c44708-0 | RUNNING | 240.22.0.223 (eth0)   |      | CONTAINER       | 0         | pirx     |
+---------------+---------+-----------------------+------+-----------------+-----------+----------+

Am I misunderstanding the docs? Is there another way to have VMs by default?

juju version 3.5.0-genericlinux-amd64 lxd version 5.21.1 LTS