This study found no evidence for an increased prevalence of anxiety disorders or MDD

From Challenging the Myth of an "Epidemic" of Common Mental Disorders: Trends in the Global Prevalence of Anxiety and Depression Between 1990 and 2010. by Amanda J. Baxter, et al

Results

This study found no evidence for an increased prevalence of anxiety disorders or MDD. While the crude number of cases increased by 36%, this was explained by population growth and changing age structures. Point prevalence of anxiety disorders was estimated at 3.8% (3.6–4.1%) in 1990 and 4.0% (3.7–4.2%) in 2010. The prevalence of MDD was unchanged at 4.4% in 1990 (4.2–4.7%) and 2010 (4.1–4.7%). However, 8 of the 11 GHQ studies found a significant increase in psychological distress over time.

Conclusions

The perceived “epidemic” of common mental disorders is most likely explained by the increasing numbers of affected patients driven by increasing population sizes. Additional factors that may explain this perception include the higher rates of psychological distress as measured using symptom checklists, greater public awareness, and the use of terms such as anxiety and depression in a context where they do not represent clinical disorders.

Another summary indicates that there is perceived increase in levels of anxiety but that the more rigorous the application of standard definitions of the various conditions, the more the effect disappears. In other words, there is an increase in self-reported mental disorders but not in mental disorders when using rigorous definitions and diagnostics.

Why is there such a strong sense that anxiety is increasing even though we cannot see such an increase when measure objectively?

I think it is still an open question. I suspect that the researchers are correct but I also suspect that there is a rise in amorphous anxiety that is not subject to diagnostics. People are fretful.

I suspect that there are some other factors that influence this perception of increasingly anxious times (despite all socioeconomic measures being dramatically better than they were even thirty years ago.

Several hypotheses. All speculation.

A more connected world, especially a more socially connected world, probably facilitates more rapid and more extensive contagions of mood affiliative beliefs. Anorexia, tattoos, social justice beliefs, etc. all probably have some social transmission element.

The dominance in some parts of academia and elsewhere of the social justice victimhood hierarchy also likely creates an incentive towards self-indulgence of behavioral/psychological disorders. If my status depends on my victimhood and I am otherwise healthy, it creates an incentive to boost status through professed disorders.

There are commercial incentives to call into existence an otherwise unrecognized, undiagnosed market.

To the extent that the regulatory arena dispenses aid (money and services) based on degree of victimhood, there is a further incentive to self-diagnose anxiety.

Perhaps it is a variant of Freud's theory of the narcissism of small differences. As society becomes increasingly prosperous, it becomes increasingly difficult to establish clear hierarchies based on consumption. In most social environments it is unclear who is really rich and who merely appears rich (but is deeply in debt). If the range for signaling status is constrained, perhaps anxiety is the means to differentiate ("I am working under such stresses")


Possibly there is some form of Munchausen syndrome at play (AKA Factitious disorder imposed on self).

That is not to discount the reality of some of those conditions. Simply to acknowledge that there are systemic pressures in place to call forth self-identification of a condition not otherwise diagnosable.