Amaysim promotions

I notice on OzBargain that Amaysim has been continually dropping prices on their 6 month 2GB introductory plans.

The 2GB unlimited plan is nominally $25/28 days.

Back in June they ran a 10FOR6 promotion that gave new customers their first 6 recharges for $10 instead of $25. On top of that they offered $32 cashback, effectively bringing the total price to $28 for 6x28 days, or $4.67/recharge. https://www.ozbargain.com.au/node/311865

Since then they have run repeated promotions on Groupon. In August the price was $36 for 6 recharges, falling to $24 in September, and today it's under $19.95. For October there has been a Groupon promotion pretty much every week.

August https://www.ozbargain.com.au/node/322510
September https://www.ozbargain.com.au/node/330720
October https://www.ozbargain.com.au/node/336357

Anyone understand the thinking behind this?

On one hand I get the proposition that some % of these signups will continue beyond the introductory period and the introductory pricing is simply cost of acquisition. But another part of me watches the price keep dropping and wonders if it's an indication that customer growth is totally stagnant.

ARPU already declined 11% between FY16 an FY17 ($25.24 -> $22.46).