Anyone can use an algo and purchase one share mate, it just...

Anyone can use an algo and purchase one share mate, it just wouldn't do you much benefit as you're not trading large sums of money. It's not exclusive to anyone, if you want to fork over the funds to access it you can (again, it wouldn't be worthwhile for you)

How do you suppose super funds etc who need to purchase billions of dollars of shares do this without incurring significant market impact cost? There's no magic button they can press to buy or sell a million shares in one go, they need to distribute orders over many small trades. It makes no sense to pay a highly paid and highly skilled trader to do such a simple and repetitive task, hence bots. Automation has become a part of all aspects of life, institutions are businesses, why should they be excluded from the benefits of automation (particularly when their need to make such large trades is largely due to compulsory superannuation which directly benefits ordinary people)