You are correct in that the IT profession liaises and interacts with people from many industry sectors and disciplines every day. The could be users of their services; external customers, who come from any walk of life; suppliers of IT and other equipment; and those in areas such as finance and marketing which administer and publicise IT.
There is no one single way to distinguish which industry sectors are in the most demand. This is swayed by a number of factors ranging from the political climate through to what's trending on social media. One could argue that, at present, COVID-19 is predominant in our news fees and so the medical industry is in huge demand right now, but then the stock markets are reacting to a health pandemic and so therefore there are people needing sound financial advice which makes this an in demand sector this week. Every year, on an annual basis, people need to complete taxes, so accountancy is in demand for the 1st 3 months of any given year. Trends change very rapidly, and there is no way to predict this.
The only safe prediction I can make is that the world is placing an increasing reliance on IT (as it has done for the last 30+ years), and that, whilst IT will continue to evolve, the demand for IT skills will always be present in some way, shape, or form.