Julie : Yes, it's always cost.
When the Medicare law became effective in 1966 hearing aid costs were not significant and not included in the law. Each time there has been a push to include a new coverage, whether it be hearing aids, dental, vision, Huntington's disease, etc. the cost has persuaded Congress not to expand coverage in most cases. The biggest exception was Part D coverage which became effective in 1996 and has, unfortunately, ballooned in cost so much that drug price reduction is part of the Biden budget plan for the coming year. And new coverage for hearing aids, dental and vision are also included in that plan. All subject to debate in Congress.
With respect to insurance plans covering hearing aids there has been a trend in recent years, as described in this thread, for coverage by Medicare Advantage plans, other types of insurance plans, and the VA. Usually not 100% coverage but significant savings off list prices.

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