If you're investing in an actively-managed ETF (or mutual fund), you're paying for someone to, well, actively manage the fund by buying and selling based on market conditions. If you believe that the manager can beat the market by buying when a particular stock is low and selling when it is high, it makes little sense to wait for the fund/ ETF to periodically disclose its positions and re-balance your portfolio based on that. If the fund manager is beating the market, by the time you know that they bought a particular stock, the reason for buying it may be totally gone (i.e. the stock was temporarily depressed, the manager bought it then, you find out after the stock has recovered). If the manager is beating the market, replicating their trades at a lag should significantly underperform the fund/ ETF.
Even with only 30 stocks, you'll incur plenty of fees to trade. If you rebalance every quarter and assume that you need to make one transaction per stock per quarter, that's 120 trades a year (10/ month). Depending on where you do your trading, it wouldn't be shocking for that to cost $5 a trade or $600 a year. If you've got a $100,000 portfolio, that's a 0.6% expense ratio for an inferior return. Of course, the exact cost will depend on the broker but that's probably in the ballpark of what you'd pay. Some brokers will give you free trades and make up for it by making a bit more on the spread or give you free trades based on maintaining a relatively large balance but there is going to be some level of cost. If you want to trade at the same frequency that the ETF/ fund does in order to track it more accurately, that's just going to increase the cost.