You can only buy stuff if you know that stuff is aligned with what you need.
Further, you need to consider that the stuff you buy also needs to aligned with your needs over time.
However, you also need to consider this when building stuff.
The alignment is the tricky thing it is easier to achieve when building in-house as long as you engineering is up to the job.
Also, note that building in-house doesn't mean engineering "from scratch". Usually it means use lower level components over higher level components/services.
Further, you need to consider that the stuff you buy also needs to aligned with your needs over time.
However, you also need to consider this when building stuff.
The alignment is the tricky thing it is easier to achieve when building in-house as long as you engineering is up to the job.
Also, note that building in-house doesn't mean engineering "from scratch". Usually it means use lower level components over higher level components/services.