CDC had stated that most healthcare providers because that older adults with depression is just a natural reaction or a natural process in aging. As a result, healthcare providers see no point in seeking treatment for their depression. Furthermore, the symptoms that arise from depression can be mistaken as symptoms for other illnesses like dementia.

https://www.cdc.gov/aging/mentalhealth/depression.htm

https://www.health.harvard.edu/newsletter_article/Recognizing_and_treating_depression_in_the_elderly

I think geriatric depression is prominent a lot of times due to the stigma around mental health, especially in the older generation. People of older age are often less exposed to the knowlodge about mental health and thus is afraid of seeking help. They also don’t want to seek help from theit children because they might feel uncomfortable or they don‘t want their kids to be concerned.

In Korea, there is a stigma of sanatorium, especially among elderly patients who are active patients of depression. Sanatorium, as a medical facility for long-term illness, can differ significantly depending on your economic status. In Korean media, sanatorium is portrayed as a negative thing, although there is nothing wrong about reaching out to seek for treatment and help. I think the STIGMA plays a big part.

Also remember that the signs of depression can also be hard to recognize. Many older adults assume that their decreased motivation, weight loss, unexplained aches, sleep disturbances, etc. (all symptoms potentially caused by geriatric depression) are completely normal, and are linked to natural aging. Because they may not suspect there is anything significantly wrong with their mental state, this prevents them from researching treatment.

https://www.helpguide.org/articles/depression/depression-in-older-adults.htm/

Adding onto @vpathy20 's point, mental health is something which has only been destigmatized in popular culture in recent years -- for generations that grew up learning that mental health was less valid/serious than physical health, it's not hard to see how you can end up with an entire generation of individuals who don't realize the importance of their mental health concerns.

Within the older generation, there is a misconception that being mentally ill is the same as being weak. For them, the depression or anxiety is a sign of personal failure, only exacerbating those conditions.

Unfortunately, in America, at least, the stereotype of a "crazy old person" seems to pervade the majority of our society. For whatever reason, we seem to have this idea that most people become mentally challenged as they grow older, and thus, when elderly people do develop mental illnesses, it's seen as a natural process. While issues such as dementia do tend to come with old age, depression is not something exclusive to the elderly, and we should begin to approach it with the same attitude that we do for people of other ages.