I was tangentially involved as a consultant when a major bank bought a few billion USD in GCP services.

Others have mentioned whole 50 person deal teams from both sides, multi year processes, all of Google’s most senior execs pressing the flesh etc.

But to your question this type of deal usually goes beyond even the C Suite, to a companies board and shareholders. The bank I was involved with held an ‘Extraordinary General Meeting’ for reps of major shareholders, to present its case and get sign-off. This part of the process was actually the longest, it took ~6 months.

That was because the shareholders of the bank had interests to be accommodated, for instance one of them was also a major holder of Amazon stock so they had a vested interest in having the bank choose AWS. They needed to be worked around or convinced choosing GCP would create more value for them than portfolio synergies.