There’s a few factors at play, which the article rather rambles around a bit.

• vet clinics are increasingly owned by private equity groups. This is primary in recent years, and linked neatly to the “untapped market potential” of the next item
• people are more willing now than ever to spend money on their pets - “pets are family”, “I’m a pet parent”. I heard about a hip replacement in a senior Guinea pig, an animal with a lifespan around 6 years.
• medical costs are expensive, and in countries with single payer or public healthcare, a lot of those costs can be transparent (for humans) which leads to sticker shock “how can the blood tests be £150, my GP doesn’t charge!”