Visual Studio Scaffolded controller actions

When using the "Add Scaffold" to create a new "API Controller with actions, using Entity Framework" on as ASP .NET Core 1.1 Web API, it generates the following:

// GET: api/Users
    [HttpGet]
    public IEnumerable<User> GetUsers()
    {
        try
        {
            return _context.Users;
        }

        catch (Exception ex)
        {
            _logger.LogError(LoggingEvents.GENERAL_EXCEPTION, ex, ex.Message);
        }
    }

    // GET: api/Users/5
    [HttpGet("{id}")]
    public async Task<IActionResult> GetUser([FromRoute] int? id)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        var user = await _context.Users.SingleOrDefaultAsync(m => m.UserId == id);

        if (user == null)
        {
            return NotFound();
        }

        return Ok(user);
    }

    // PUT: api/Users/5
    [HttpPut("{id}")]
    public async Task<IActionResult> PutUser([FromRoute] int? id, [FromBody] User user)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        if (id != user.UserId)
        {
            return BadRequest();
        }

        _context.Entry(user).State = EntityState.Modified;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!UserExists(id))
            {
                return NotFound();
            }
            else
            {
                throw;
            }
        }

        return NoContent();
    }

    // POST: api/Users
    [HttpPost]
    public async Task<IActionResult> PostUser([FromBody] User user)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        _context.Users.Add(user);
        await _context.SaveChangesAsync();

        return CreatedAtAction("GetUser", new { id = user.UserId }, user);
    }

    // DELETE: api/Users/5
    [HttpDelete("{id}")]
    public async Task<IActionResult> DeleteUser([FromRoute] int? id)
    {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        var user = await _context.Users.SingleOrDefaultAsync(m => m.UserId == id);
        if (user == null)
        {
            return NotFound();
        }

        _context.Users.Remove(user);
        await _context.SaveChangesAsync();

        return Ok(user);
    }

    private bool UserExists(int? id)
    {
        return _context.Users.Any(e => e.UserId == id);
    }

The first thing that popped to me when I looked at the code that Visual Studio generated, is that all the methods return a Task, and all are async, with the exception of the first one: public IEnumerable GetUsers()

Is there any reason for this? I mean, what if there is an error? It should be able to return an 500 Internal Server Error, instead of a null? And why isn't this running asynchronously?

Thanks