Why access is denied?

Because the I/O control code SMART_RCV_DRIVE_DATA is defined in the winioctl.h header file as

#define SMART_RCV_DRIVE_DATA            CTL_CODE(IOCTL_DISK_BASE, 0x0022, METHOD_BUFFERED, FILE_READ_ACCESS | FILE_WRITE_ACCESS)

Note that RequiredAccess parameter in the CTL_CODE macro is FILE_READ_ACCESS | FILE_WRITE_ACCESS.

How to fix it?

In order to fix the problem, you should call CreateFile() function specifying dwDesiredAccess as FILE_READ_DATA | FILE_WRITE_DATA, not just GENERIC_READ. Like that:

HANDLE hDrive = CreateFile(drivePath.c_str(), FILE_READ_DATA | FILE_WRITE_DATA, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, 0, nullptr);

GENERIC_READ | GENERIC_WRITE also will work:

HANDLE hDrive = CreateFile(drivePath.c_str(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, 0, nullptr);

Running it as Administrator is unnecessary.