You mean that it is show in list format on the console?
That is due to the size and number of properties.
When you export it should be in CSV format.

$report = foreach($esxcli in Get-VMHost | Get-EsxCli -V2){
    $esxcli.hardware.platform.get.Invoke() |
    Select @{N='VMHost';E={$esxcli.VMHost.Name}},VendorName,ProductName,SerialNumber,
        @{N="BIOS version";E={$esxcli.VMHost.ExtensionData.Hardware.BiosInfo.BiosVersion},
        @{N="BIOS date";E={$esxcli.VMHost.ExtensionData.Hardware.BiosInfo.releaseDate}}
}
$report | Export-Csv -Path .\report.csv -NoTypeInformation -UseCulture