Upon investigation Hosting site referred us to this Q&A
Information on Disabled PHP Functions on Personal, Business, Premium and Reseller services
A small number of PHP functions, including exec() proc_open() and system() are disabled on our Personal, Business, Professional and Reseller hosting servers. As these are shared hosting servers, they contain multiple cPanel accounts and clients on each server. To maintain the security of our clients, their emails and websites (almost all of which are businesses) we have to maintain a strict security policy and aren't able to enable them for any individual users or cPanel accounts.
The list of disabled functions is based on up-to-date security recommendations by the cPanel company. Almost all hosting companies which use cPanel will have a similar security protocol in this regard.
PHP is regarded as the most insecure technology on the internet,which makes it dangerous, especially as most websites are built using PHP. Web builders like WordPress, Joomla, Magento and most others are essentially applications made using PHP.
You can see how often a new PHP hack/exploit is discovered here (at least 1 each month) by checking this link.
The functions are most commonly used by minor plugins and themes for WordPress, Joomla or other Content Management Systems. The best option in this case would be to look for an alternate plugin or theme which doesn't have this requirement.
Can you please advise what is affected by these restrictions? Are there workarounds?